Say your script is called run_time and it's location is /home/me/ you would type in:
30 20 * * 1-5 /home/me/run_time > /home/me/run_time.log
the first value(30) signifies the minutes, the next hours, days ,month, way of the week. So in the example I'm setting this to run at 9:30pm monday thru friday.
HTH,
jocasio