Well, sure, it’s obvious now.
I’m a married guy and I’d say yes to going to that concert. Good taste in music.
If you are not firmly in the friend zone, if I were you, I would ask her in two weeks when you see her after curling practice again. Keep it really simple. “I have tickets to see Postmodern Jukebox next month, would you like to (get dinner/have a drink) and go with me?” You can tweak that to better fit your personality, but be as straightforward as you can. You want to avoid confusion about whether it’s a date or not.
If you are really bad at reading signals, it’s perfectly okay to ask her something like 'Would you like to go out (on a date) with me? I have tickets to …
I know you don’t want to hear this, but be prepared to act gracious if she says no. Everybody, man or woman, has been told no before. It’s not fun but you can move past it and try elsewhere.
One final thought. If she does say yes to the date, masturbate before you leave your house. You’ve been waiting over a year to date this woman, so get the whole premature ejaculation thing out of the way. Don’t worry, everyone does this on first dates. Trust me. 
Good luck!
In my ever so humble opinion, keep it casual, but be direct enough that you indeed tell her that you want to spend time with her. And then accept her reaction, and let her make the next move.
I even think it’s okay to let her realize that you are romantically interested in her, as long as you don’t make it weird if she politely declines.
So, the next time you see her, I’d suggest something simple and direct:
“Hey, Hortense*! Great to see you. Say, I’ve got two tickets to a concert next month. I’d love it if you’d join me!”
She may light up. Or, she may make some weird excuse. Or sort of seem ambivalent.
They key is to accept her reaction, whatever it may be, and don’t try to change it. If she goes, “That sounds amazing!”, you’ll feel like a king. But if she goes, “Oh, uh, gee, I may have a thing with my cat…” just smile and go “Hey, no worries. If you ever want to get together, just let me know.”
If you leave it at that, you have nothing to be embarrassed about, and you’ve allowed her to politely decline without having to feel weird around you.
And if she ruminates on it, and starts to realize how cute you are, and changes her mind, you’ve made it casual and easy enough for her to come back to you in a few weeks and say something like “are you still looking for another person to go to the concert with?”
*Just a guess
It’s completely true - I once asked a woman if she could control herself at the sight of my naked torso.
Next letter up is Pi; that variant will never end.
I’ve seen them a couple times, just ridiculously fun. The only problem is I don’t always know the originals that they’re covering.
I do have the perfect pair of shoes, though; just what the well-dressed man was wearing in 1933.
Yeah, that part I can do. My worry is more that she’ll say no, and I won’t know if it’s a genuine conflict or an excuse; she works in health care, so she may be staying extra isolated, or just not want to be out late on a weeknight. Or that she’ll say yes and not realize it’s a date.
Was she laughing when she said no? That’s one of those hard to read situations.
Me either. They are just so great, both music and voice wise, it doesn’t matter if I don’t know a song here or there. It’s also a good date choice since you won’t be blasted away by the music so much you can’t hear each other when it’s over.
In my experience, a no means no. If she’s interested in you, but not in going to a concert, she will likely suggest an alternative like dinner or something you can do on a weekend.
Since this seems to be a worry for you, I think you should use the “Would you like to go out with me next month, I have tickets to a concert.” It allows her to know exactly what you are asking and she can respond accordingly.
This is really well put. There is nothing for you to be embarrassed about in asking, no matter what the answer. The last thing you want is for it to be awkward for either one of you to see each other socially anymore. It is kind of strange to see it coming from a criminal mastermind tho. 
It’s too bad she has been burdened with the name Hortense. Maybe she has a really nice middle name. I’d put some thought into a nickname, or maybe just be prepared to call her Honey or Dear a lot.
For something like a concert, ASAP.
It’s something that needs that specific timeslot booked, and can’t be spontaneously rescheduled if there’s a clash, like a dinner, movie or sex can.
This would be a good line to have handy if you approach a woman at the bar and she says “whatever you’re about to ask me, the answer is no”. 
I would be really put off by this. Just ask me if I’d like to go. Don’t give me a deadline, or twll me that you have a backup plan.
If I’m a decent human being I’m not going to hem and haw for WEEKS. I don’t need to be told not to do that.
Tickets to a thing have an inherent deadline. Asking someone to an event is kind of a big ask. I don’t see why it would put anybody off to say “I have these tickets, don’t feel committed to say yes, and don’t feel like you need to give me an answer right away” would put anybody off, I think it would take the pressure off by not putting the person on the spot.
But don’t worry, I’ll make a note not to ask you next time I have tickets to something
I think agonizing about exactly when to ask someone to a special concert is a bit silly, frankly. This isn’t about logistics and scheduling.
Unless I’m mistaken, OP’s underlying agenda here is how to ask a lady out on a first romantic date - someone that he’s already friends with in a group setting. I gather that there have not been unambiguous signals from flirting etc., so he’s genuinely uncertain if the interest is reciprocated, and probably does not want to make the social situation awkward if the answer is “no”.
The first date should not be a concert, it should be dinner or drinks, some situation where they can talk and get to know each other better. He should ask her out on that first date right away - directly, confidently and unambiguously. It should not involve any grand romantic gestures like flowers or Valentines Day or a special concert. It should not be asked in any situation where she might feel even slightly uncomfortable - two people alone in an elevator, say. Just something very straightforward like: “I feel like we get along really well together. Would you like to go out with me next week - just the two of us, for a date?”
Almost certainly, she already knows him well enough to know if the romantic interest is reciprocated. There is nothing to be gained by agonizing over the timing of asking, or by being vague or indirect - none of that will change her answer, and it only creates the potential for misunderstanding and awkwardness, perhaps even the potential that she might start seeing you as creepy if she’s not interested. But there’s absolutely nothing creepy about asking confidently and directly, once. I would avoid specificying an exact date in the initial question - that just creates the potential for ambiguity about whether she’s saying “no” or whether she has a genuine conflict with a prior engagement. If she is interested but genuinely busy all next week, or has COVID concerns about restaurants, she will open the door to some other kind of date in her answer. Anything that doesn’t clearly leave the door open to continuing the conversation about a suitable first date in times of COVID is a “no”. (A “no” doesn’t rule out her changing her mind about you later, but then the first move would be down to her.)
If the first date works out, there’s plenty of time to invite her to the special concert for a second date.
No, it really is just the timing I was wondering about.
Have you been reading the other thread?
I don’t see the concert as that big a deal. It’s not like opening night on Broadway, just a fun, and slightly quirky, band.
Is it supposed to be a first (romantic) date?
I have not been reading the other thread, or don’t know what other thread you mean. Link?
Is it meant as a first romantic date? If so, I agree that a concert isn’t the best choice, and I like Reimann’s suggestion. Make it clear you are asking her on a date, details TBD if she wants to go on a date with you.
If you are just asking a friend to go to a concert with you, and it’s not meant as a first romantic date, ask her ASAP, since the precise time matters. That gives you the most time to find someone else if she’s busy then. She can put it on her calendar if she says “yes”, and you can remind her once, close to the event.
Ideally, yes. Sometimes you have to buy tickets for an event months in advance to get them at all, but inviting someone that far ahead seems like it could be awkward. That’s really all I was going for in this thread. The fact that people have shared such differing opinions means that there’s not a simple answer.
All the rest of the advice has been interesting, and well-intentioned I’m sure, but if I haven’t figured out some of that stuff by now, I never will.
Then I wasn’t misunderstanding the situation, so I stand by everything in my post above.
In my experience, it’s not that easy; there is always ambiguity, and a chance to misunderstand.
It’s a big deal for a first date. She knows you as a friend already, and she’s either romantically interested in you or she’s not. Your initial objective is really quite straightforward - to get that information from her brain to your brain, using words. Any kind of grand gesture for a first date adds nothing, and can be counterproductive and even seem creepy, as though you think relationships are transactional, that she will agree to go out with you only if you make it worthwhile for her with something special. If she wants to go out with you, it’s because she likes you, not because she likes concerts.
So you seem to have taken away from that “It’s impossible to clearly establish romantic interest, therefore I shouldn’t try to do so.”, and have lived by that for 25 years. Whereas the rest of us are probably thinking either (or both) “Wow, she was completely oblivious to your clear intentions”, or “For some reason your intentions weren’t as clear as you intended.” Which is why people are saying to use the word “date” when you do ask her out.
Note that in this thread, it took a while for you to clarify that you do in fact have romantic intentions in asking her out. If you’re just as unclear with the people you’re asking out as you are here, it sort of explains some of your difficulties.