Hi Joe,
The estimated run times are affected by the acceleration setting under CNC/CAM Settings which you will want to set to your machine's actual acceleration speed to make the run times more accurate :]
Unfortunately there's really no way to 100% accurately determine what the runtime will be for all possible machines in the world simultaneously, one can only hope to get close enough to be useful. It's at least nice to know if something is going to take 30 minutes vs 30 hours!
- Charlie