A useful tool anyway, is Kiwi CatTools. Primarily we use this to grab the configs from all the Cisco routers and switches on an hourly basis, and it keeps any that have changed.
It also allows you to execute commands and config changes, on a timed basis. What you can do is set this up to telnet (or SSH) to all the switches, and execute the commands to turn off the PoE in the evening, and then run another job in the morning to turn them on again. The link telling you how to do this is at http://www.kiwisyslog.com/kb/how-to:-use-kiwi-cattools-to-modify-my-device-configuration/
and the link to download a 30 day trial is at the top of the page, under Downloads.
It does cost money after that, $750 for two years, but this is a very useful tool for managing a large number of Cisco boxes.
I hope this helps