The performance tab gives you some clues as to how many people are busy on the system at a time.
Despite having "world-wide" users, the simple math shows that it's easy to find times in the day, or times in the weekend where activity is very low. Early morning in Australia is Evening or night in the US and middle of the night in Europe/Asia. Because the land masses are not spread evenly, when it's midday over hawaii, pretty much everyone else is not working.
Clearly it's not a good idea to do your maintenance when others are working.
cheers
Bruce