Take Turns is a FREE utility that allows you to divide up time on one computer any way you see fit among a group of users. You can set up virtually an unlimited number of users and schedules. Select the schedule you wish to run and the program will alert each user when their time is up and that the next user is to proceed.
This utility was primarily designed for families with children who need a way to alot usage of their computer in a more equitable manner among their children.