cool down time could go even up much more. People who want to goto holiday or on a long business trip or for what ever reason they change their living area for a longer time, would know also long before that. 3 days seems reasonable as minimum if you think of business trips on short notice though(who takes his laptop with him onto a buisness trip?). No-lifers normaly have also a fixed daily habits and things may come up but rather without so much planing, at least in my case, but there i wouldn't vote to increase the no-lifers chances but those who have a life and want to keep it!
I for myself, have only changed the nighttime once in each strategus sofar, so a high cooldwon time isn't even something which came to my mind could be a problem.
A cooldown between 3 days and 2 weeks seems appropriate.
And 14 hours would give most of us the opportunity to regulate the bare minimum of things we need to do daily without being too concerned about strat.
Still an option for rank 10 leaders, to set a default nighttime for all in the faction, would crown this system. Each member would still be able to adjust it to their needs, but noone would be left out and therefor, there can't happen the same old shit.