What scheduling server are you using? If you are using Platform Process Manager / LSF, then there are housekeeping tasks you can do to see if that reduces delays. It's also possible you might be reaching some configuration limit on simultaneous flows and new ones only start when current ones complete. I recommend you open a Tech Support track to investigate further.
The SAS Users Group for Administrators (SUGA) is open to all SAS administrators and architects who install, update, manage or maintain a SAS deployment.