survey of maintenance time

Dear administrators: I am a PhD student from Univ of Oregon. We are studying the characteristics of Internet routing instability. I have a very simple survey for the administrators. Do you mostly do the system maintenances during the weekend in order NOT to interfere network usage during weekdays? Here I mean maintenances like change routes, replace devices, change configurations... The more response, the better :) Your cooperations are greatly appreciated! Zhen Wu