My gut says it either arrives in the originally quoted window or the very early portion of this new one. Supply chain issues haven't gone away - and Apple doesn't have control over how quickly its shippers move things.
When I ordered my MBP, it sat in Preparing to Ship for 5 days I think? Its all a process. My gut says PTS status means, it's left the production line, and is sitting on a pallet or in a shipping container awaiting pickup by the shipper - which is likely UPS. (This MBA is for my wife).