Is it easier to break into the military base at night?
Solution 1:
I don't think day/night makes any difference.
I've flown into the base multiple times (day and night) and have always gotten the same reaction. You have to fly close enough to the ground inside the base perimeter to trigger the wanted level of 4 stars. If you hover high enough above the base they do not seem to care.
In any case, it seems like landing a helicopter near a jet is the easiest way to obtain one.