OWB has the By Clause to create complex schedules. Imagine you have a near real time ETL process that needs to execute every 15 minutes between 7 am and 0 am. You don't want this schedule to execute during the night because other maintenance operations such as stats gathering etc. need to run.
Create a schedule with your start date and a start time of 7:00:00 am. As repeat expression for this job specify minutely and set the frequency to every 15 minutes.
Specify the By Clause to create the complex schedule: click on By Hour and enter 7 am - 0 am.