At what time before the end of the set the *system block us from attacking ?
4 hours before the end ? 6, 8 ?

In my experience it's a diminishing window based on NW that starts to close about 6 hours out.

ie the closer to end of game the closer you must be in NW to be able to attack - eventually t seems you can't attack at all regardless of NW

6 hours for GDI

After that you can’t attack anyone who hasn’t attacked you

Thanks