20 minutes after the hour.
 

20 minutes after the hour their guard could be down.
Creatures of habit including Armies structure their timetables such that 5pm is better than 5:05pm for changing of the guard, therefore 5:03pm to outwit us?
Anyway by 5:20 the excitement is generally over at camp Hostile and is a good time to evade or attack them.

what?

The superior man, when resting in safety, does not forget that danger may come. When in a state of security he does not forget the possibility of ruin. When all is orderly, he does not forget that disorder may come. Thus his person is not endangered, and his States and all their clans are preserved. (Confucius)

erm....what?

"Rules of War" by General Lostme Rice?
Thing is bad guys read the book too, including the nips in WW2
so they were easy pickings for those who read the stuff, lying in the sun on PNG.....lol

What we know is our undoing, to stay one step ahead of what we know, that is...THE TWILIGHT ZONE