No. Putting posting date in the business rule won't trigger it during asset master creation, the only event (+ modification, of course) upon which FM assignment could be updated in the asset master data. Posting an acquisition could not serve as triggering event.
Think of reading asset master data and taking some other date field, but coming from asset and which is filled upon creation. You can access the master data using FMDT_READ_MD_ASSET funciton, for example.