Bukkit

Define a start time and a speed modifier per world. Set a suitable refresh rate for the performance of your server.

Speed could be increased/decreased up to 20 times or match UTC time with offset to local time.

Day and night can be set to different speed values, which can be great for RPG or some mini-games.

Worlds list is actualized and timers are synchronized on each server startup and reload.

Timers and speeds can be modified or re-synchronize with in-game commands or reloading after manually changes.

Sleep can be authorized, forbidden or linked with some other worlds. 

A specific time offset can be defined for each player.

TimeManager can schedule commands that run at a time specified in the cmds.yml file. Scheduled commands can use the placeholders described below, with the exception of {tm_player}.

This plugin override the vanilla "/time" command. The command to change a single world timer is "/tm set time [ticks|daypart|HH:mm:ss] [world]".