Do they rewards have to be claimed every day or will they be available later? Basically I'll have 500 energy in 2 days but I'd like to wait until the weekend to claim it... can I wait or will I lose it?
They get claimed automatically on login. You can choose to not log in to delay, but you won't progress to the next day's reward until you claim the current one.
Also if you never log out and don't go into the daily log in rewards page, you can delay it until the next day, at the very least. I've never tried to get past the next days reset, though. :P