Chronos manages time. You can schedule a function to be called in X seconds, with or without an id. You can request a timer, which tracks the elapsed duration since the timer was started.

You can also create Tasks - functions which will perform a complex operation over time, reducing system lag if used properly.

Please see below or see http://www.wowwiki.com/Chronos for details.
Changes :
$Rev: 1380 $
- This patch can be called the Garbage Collection patch. The Chronos core functions are not just faster, they're also now completely free of garbage collection impact. This is important because when garbage collection occurs, the client will pause for half a second, which is certainly not something you want happening in PvP. Base UI + Chronos + Sea has ZERO garbage collection impact when idle.
-Updated some localizations for spelling.
-Updated scheduleByName to handle correctly updating the time for currently scheduled events without redefining the callback function.

$Rev: 1653 $
-Invalid key for 'next' error fixed. (CORRECT)
-Chronos afterInit changed to be compatible with 1.5.0 patch.
-Updated TOC to 1500
-/in, /pause, and /delay commands will now function both with and without Sky, however they will only appear in the /help list when using Sky.

$Rev: 2250 $
- Chronos no longer allows events to fire while you are zoning in and out - this was causing some clients to disconnect. Furthermore, it could cause addons like Sky to fire too many events while zoning, which could fill up your event queue.
- Optimized a number of highly used functions to be more Garbage Collection friendly by avoiding "..."

$Rev: 2424 $
-Fixed a bug where the list of arguments to be passed to a scheduled function was getting truncated if it included a nil value. This was causing AIOI's mad GC usage.
-Fixed another bug where the list of arguments never got passed to functions scheduled using Chronos.afterInit.
-Updated TOC to 1700

$Rev: 2777 $
-Added Chronos.scheduleRepeating(name, delay, function) which calls functions (without arguments) every X (delay) seconds. Useful for simulating OnUpdate for efficency (ex delay of .1 would call the function 10x/sec). Recall this function to update the time. (ex Chronos.scheduleRepeating(name, delay) )
-Added the Chronos.unscheduleRepeating(name)
-Added Chronos.IsScheduledRepeating(name)
-Updated TOC to 1800

$Rev: 2778 $
-No longer requires Sea
-Updated TOC file loading method
-Made schedule calls a tad more efficient
-converted OnUpdate while loops into for loops for efficiency

$Rev: 2781 $
-Fixed invalid key for 'next' bug. (INCORRECT)

$Rev: 2782 $
-Fixed index number bug (O.o) (INCORRECT)

$Rev: 2789 $
- Merged the repeating and byName lists for OnUpdate efficiency. (Note: this also means scheduleByName and scheduleRepeating can no longer have the same names)
- Added Chronos.flushByName(name, when) - Updates the ByName or Repeating event to flush at the time specified. If no time is specified flush will be immediate. If it is a Repeating event the timer will be reset.
- Added Chronos.debug(booleanEnable) for debugging. This also means that the normal OnUpdate function has been shortened and is now slimmer/quicker.
- unscheduleRepeating and isScheduledRepeating now mirror unscheduleByName and isScheduledByName for backwards compatibility.
- Fixed 'next' error that was cropping up in the for loops when niling before calling a local var. (INCORRECT)

$Rev: 2789 $
- REALLY fixed 'next' error. For future refrence it was incurred by removing the current key/value pair from a table while itterating over it with a for loop. Unfortunetly no one wrote this down before, so the sam problem someone else fixed was recreated on accident in an attempt to make more efficient. (CORRECT)