Yes, unless the buyer told you in advance that he was planning on buying another item and asks you to hold off shipping, it is important to get purchases out as soon as possible.
EBay even gives you a small boost in Search for short shipping times. And that overlooks the question of DSRs.
Some sellers moan that they cannot get to the PO very often. However, if you use Paypal labels or even keep a stock of postage stamps on hand, you can drop any mail, including barcoded/ DC services, into the nearest postbox. My DD does this even though the postbox is actually at the PO since she had a blowup with a grumpy clerk a couple of years ago.