Hi,
you could schedule a job or trigger an event only on weekdays, and then let your PC run after that job/event. But to schedule this job you will have the same problem :-)
The easiest way is to create a factory calendar in BW which is NOT used in ECC.
Txn SCAL is what you're looking for. Select factory calendar and click edit. then create a new calendar and don't enter a holiday calendar. Select your working days and you're good to go.
regards