Interesting - as soon as I read the thread title, that’s the seven days I thought of.
Christianity - particularly Pauline Christianity - has some positives over other contenders: no ethnic distinctions, low barriers of entry (don’t have to get circumcised), and ample promised rewards (in the afterlife). Not sure which other religions might apply - Buddhism, perhaps? Of course, it would have to be something that Constantine knew about…
I do kinda like this one - especially if you move it to the entire week of 28 June - 4 July, when Kaiser Bill decided to give the Dual Monarchy his blank check. War wasn’t inevitable before then; it pretty much was thereafter (although the Czar had a chance to keep it localized as well).
If we go into prehistory, I think the first seven days after the Chicxulub asteroid hit probably qualifies.