Brilliant idea, please do this as often as helpful.
Thank you;
and yet somehow it didn’t help this time. 
I personally usually give a 24 hour cooling off period.
Sometimes that doesn’t help either.
I’ve seen them not help more than help, unfortunately. Any cooling off seems to be offset by people rereading what was said to get back up to speed.
Plus it’s basically impossible that people won’t get upset when they perceive one side as defending bigotry. It’s not specific to trans-related threads, and thus why having certain bigotry-related topics declared off-limits in GD helped make it a less contentious place.
Have you tried blowing on it?
I wonder sometimes if cool-off timeouts are counterproductive. A poster can easily recapture the heat of the moment by rereading the thread and on top of that you add impatience to say what was delayed and maybe even frustration at the delay itself.
I like this moderation tactic - a good counter to the “didn’t see the moderation” excuse people use.
And you think these toddler attitudes are something the mods should be accommodating? Naah, if this technique outs such petulance and stomps on it, that would be a good thing.
It seems like a good idea for the stated purpose of stopping people posting before seeing the new guidance. I’ve certainly posted a reply and only then seen a mode note, and had to hurriedly review my post to check it was still within the rules (so far they have been).
Maybe longer cool-offs aren’t so useful. Depends what the purpose is.
I think a 5 minute one is good enough to give posters a chance to see a new modnote.
As we can see that posters are typing a reply, I wanted to stop the hijack and try to prevent a warning. So Modnote and locked thread for 5 minutes. Should have been plenty to cut off what came next.
It also bought me time to add in a note to Riemann and my little disclaimer about modnotes. I probably fixed a grammatical mistake too knowing me.
Ashtura said he(?) was prepared to accept a warning for making the post. You can help people avoid breaking the rules by mistake or while in a temper, but it’s their choice if they want to break them deliberately.
Now that’s an abuse of moderator privilege. You need to suffer your poor grammar like the rest of us. 
LOL
1st: It was within the 5 minute edit window clearly.
2nd: We’ll fix grammar, spelling and coding errors for posters on request. In fact coding errors I often fix upon seeing.