The "shipment received acceptance pending" scan is when your carrier or PO scanned the SCAN form (which I think you realize, but I'm including for the benefit of others reading).
The next scan depends on your PO and whether they scan before sending packages out the door, or whether they leave items to be scanned by the first sort facility, and also depends on that facility's processing times and backlog.
Generally my local sort facility scans late night the same day I ship, but if they're backed up it can take an extra day.
Either way, the scan you're already seeing is enough to satisfy eBay for your on time shipping performance.
