Periodic data save (or how to get a timer server side)

I'm have a command mod that saves it's data in NBT format.  It's stored in memory for performance reasons, but I would like to write it to disk say every 15 minutes.  The math is no problem, the problem is I can't seem to find a way to get a timer event notification server-side.  The Timer class is client-side only.

Is there a tick event or some other less obvious way to achieve this?  Or is there a way to tap into the /save-on command so I can write the data back out?  I'd hate to have to write the data every time a user makes a change.

Thanks!