Do you have to join Raids in the first 24 hours?

That’s a thing, right? I told my alliance to wait before getting in to Nightmare Raids, have a look at how it’s going for others (the YouTube community basically). But you can’t wait too long, correct?
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(2) alliance has to have setup the week for Raids prior to week starting (can’t see how it's going for other Ally’s before deciding whether your Ally should run normal vs nightmare version of raids)
(3) people can wait any # of days into the week before joining Raids, *BUT* you can not join any other AQ BG beforehand during that week (*thus what is meant by “must join day 1” really means has to be the first, and only, AQ map you join during that week)