I present to you, a rather simple mod "Time Controller"
Ever wanted to make your minecraft days last a little longer?
What it does - It adds 1 block, the "Time Block". When the block has a redstone signal it will begin it's loop of freezing/unfreezing time in order to effectively increase how long a minecraft day last for. If your experienced with redstone you can even set up a timer loop with redstone to turn this on/off. Example, using a daylight censor.
There are 2 commands to control how long each cycle last for
1) /tc timedelay # - Changes how long time is frozen for (seconds) before it unfreezes.
2) /tc cooldown # - Changes how long time is unfrozen (seconds) before it freezes.
/tc timedelay 100 - Will make time freeze for 100 seconds
/tc cooldown 100 - Will make time unfreeze for 100 seconds.
So if you have a timedelay of 60 and a cooldown of 90, during the loop, time will freeze for 60 seconds, and then unfreeze for 90 seconds, and then rinse and repeat.
It's untested, but I'm fairly certain this should work on servers as well.
If you need a visual of the timers, go into your controls and set a binding for 'Time Controller Display'. Default is Numpad 0.