PhotoPass help??

[chmurf]

So on 1st Aug, we have a photo taken, that expires on 31st/1st Sept.
on 4th Aug, I decide to activate my online account - is that photo safe until 31st Aug/1st Sept, or is it now safe for 30 days from 4th Aug (when I activated my online account?).

30 days from when you enter your ID on the website (what you call "activation", so September 4th (in that example)

So, what I'm thinking is, activate the PP+ on Day 1, but don't activate the online account until about 1 week in, if that will give me 30 days from then, rather than 30 days from when the first photo is taken.

that's correct.
If you "activate" (enter your PP+ ID) on week 2 you'll still have 30 days to edit and order.
You can even activate once your back home, as long as you're in the first 30 days since the first picture has been taken

the more you wait for entering your ID, the longer you have to edit and order.
(as long as you don't exceed the 30 days since 1st picture was taken)