It uses time before engine is at operating temp and time engine is at optimal temperature along with the RPMs reached in each stage, time at idel as well as the outside air temp to caculate it's oil change interval.
So if you did a lot of quick trips in a cold environment oil indicator will come on fast, idel a lot in traffic it will come on fairly fast as well, go on many long trips in a warm climate your oil will last a very long time.

 

Stupid question.... does the change oil prompt come standard for all JK's or is it an option?

 

Standard