Do all towns get attacked at the same time?

Yes, all towns get attacked at the same time. You don't need to stay out and auto-scavenge over night however. Remember, there are a number of ways to use your AP, including construction, scavenging (sans auto-scavenge), and Workshop conversions.

Since the primary appeal of the game is the social dynamic, there should be plenty of ways to enjoy it without having to auto-scavenge overnight.

If you can't get on your computer before the attack to get inside the gates, then just dump all your AP in the Workshop or at Construction. You can still be useful and contribute that way