Why does it take so long until the system reacts to sleepi..

My system recently developed a very nasty habit, namely that when I
press the button to sleep or hibernate, it takes "forever" (i.e. up to 3
minutes!) until the system finally indeed goes asleep, or hiberates,
resp.

What is even more annoying is, that it apparently buffers multiple
requests, i.e. if I "dare" to press sleep/hibernate again during that
time, then - when I woke it up again - it will almost immediately
sleep/hibernate again and this as often as I pressed the key. I recently
had to wake it up 4 times, since I apparently pressed "hibernate" that
often until if finally reacted. I find this whole behavior most
infuriating!

First: what could cause the system to take that long to react to a
sleep/hibernate request? Ist there some "force"-option or some timeout
that one can reduce, such that no app or driver is ever allowed to block
a system's sleep/hibernation sequence for more than, say, 5 seconds at
most?

And second: can one somehow tweak the system to NOT buffer additional
sleep/hibernation requests while it already is in the sequence?

Michael