To clean up derailments faster!
1) Create a new session
2) Edit Session
3) Click on, Clean up derailed trains
4) Change the 1 minute value to 0:00:05 or you can simply do 0:00:01.
I'm not certain if you can use 0:00:00 value, I think it has to require at least 01 on the timer
EDIT: You can only have a minimum limit of 0:00:30 '30 seconds'. It will not go lower!