When a spy has 2 or 3 hours, it is very possible that it is no longer feasible.
Imagine that I spy an area and about 40 planets appear that I can attack but I only have 15 free slots. When I can attack again, 2 hours have passed since I did the spying. And when he attacks the number 40, 4 or 5 hours have passed.
This variable of time is what I speak of. Being able to control the time in which an espionage is viable to attack.
I feel like I express myself in English, but I'm using the google translator

maybe an option in the farm session to make the espionage reports valid before "x" hours. when the time passes, a new session is started (if available)

Spy on the chosen rank.
Attack until slot complete
As they are free slot, you continue with the attacks, but it has been a while (80-100 minutes)
Those espionages I mean, that since it was spied a long time has passed and they may have become obsolete with what the attack fails.

Not sure which espionage you're talking about ?