what elements decide the duration of every operations in EAM work order?

hey guys:

      i have a question which i hope could be answered by some of your help.

      as you can see from the below screenshoot, i just added two operations and resources in a work order, both of the value of  resources assigned to the operation was 1,but when i saved the WO and changed to scheduling tab, i found out one of them last for 17 hours and another was only 1, given the situation that both of the resources value is 1, i guess there must be sth else decided the duration, hope my question could be answered.

thanks in advance!