Yeah, no. I mean sure, that’s obviously what they mean, but isn’t what it says.
If I told you I’d be at your house within 3 to 4 hours, you wouldn’t expect the window to start until 3 hours in.
And in any case, there’s no value in such a wishy-washy window: there’s no way to apply that information in a meaningful way.
Don’t add lettuce to your sandwich and you’ll be fine.
Maybe that should be included on the lunch meat label? 
Hormel might get blamed for an illness that the other sandwich ingredients actually caused. A sandwich could also include lettuce, tomato, mayo, musturd and onions.
Yes, I would, if you said something like “Starting from now, I’ll arrive within 3 to 4 hours”, like the package directions say “After opening, use within 7-10 days”.
That definitely doesn’t mean that your window of arrival doesn’t even start until 3 hours in. It means “I’ll get to you probably within 3 hours from now, certainly no more than 4.”
Somewhat subtly, if you said “I’ll arrive in 3 to 4 hours”, I’d be more likely to interpret that as meaning “the trip will take no less than 3 hours and no more than 4”. But “within” suggests “within a time period beginning at 0 and extending to maybe 3, maybe 4 hours”.
Well, I already agreed with you that the range of values makes the prescribed “window of usability” a bit wishy-washy, but I don’t agree that it makes it meaningless. The phrasing strongly suggests, and I think most consumers so interpret it, that you don’t really have to worry about spoilage potential for about 7 days after you open the package, but after 10 days you should definitely worry. How you’re supposed to assess your safety in the interim 3-4 days is, as I said, rather unclear.
But yeah, those instructions are giving some meaningful information about the spoilage timeline, even if not as much as we might like.
If you get sick from eating that sandwich I think I’ve spotted the cause.
My guess is that you assess the safety the same as you do at any other time- if it looks or smells spoiled after three days, I’m tossing it. I expect the 7 to ten days is to avoid the complaints that will surely come if the package says 10 days and it spoils after 7.
And to reassure people who eat it for 10 days without incident.
If they had just said “use within 7 days”, then that wouldn’t mean “it has to last you exactly a week”. Using it all in the hour after you open it would qualify as “use within 7 days”, as would using half of it today and half of it tomorrow, as would saving two slices for five days from now, etc.
If they say “use within 7-10 days”, then that means that it should definitely still be good 7 days later, and it’ll probably be good 10 days later, but after that, don’t count on it. Still a meaningful and sensible statement.
I think you are right. It’s just common sense and most people can understand.
The wording would have to be much longer to be absolutely literally correct and precise.