The timelapse condition would be useful for keeping your scripts in line with the timerbased system.
Since the timerbased system of PB keeps everything running at a speed that would be most consistent with 30fps, then using "timelapse=30" would make sure that line of code would only execute 30 times per second. It's an even easier alternative to muddling with timers to have certain lines only run... once or twice per second, for things like slow healing.
Remember, scripts run as FAST as they can. If your game is currently running at 134fps, then your script is being executed 134 times per second. But maybe you don't want parts of your scripts to be running that fast. You could use timelapse to ensure they only happen a certain number of times per second. It's kind of like capping a single line of code to a framerate, without altering the game's framerate.
It can be used in a multitude of ways, but the best way to use it is your own way.
AFTER-THOUGHT:
It just occured to me to go and check the code, because I honestly could not remember how I went about coding that command, lol.
This brings up a very important note for everyone.
You should make sure that your script only uses ONE timelapse command at a time. It uses an entity variable to track how much time has ellapsed since it executed last. Having more than one of them running at the same time (in the same script) would cause problems and only one of them would work (Either the one with the highest number, or the one that is higher up in the script (closer to the first line))
Example:
:state=1,timelapse=10:state=2
:state=2,timelapse=30:state=3
:state=2,timelapse=60:state=4
State 1 is fine, as it will not interfere with the other timelapse conditions (Since it is in it's own state). However, it is LIKELY that the second line of state 2 will execute first, since it is running at a higher rate (60 times per second as opposed to 30 times per second) and the script will likely end up in state 4 and never see state 3.
Hope that all made sense.
The one and only,