The seller does state a "handling time" to eBay for every listing, but eBay stopped displaying it on most listings (sometimes it still does, don't know how they decide), up to 30 days. eBay keeps track of whether the seller shipped timely and downgrades those who are late too often.
In any event the handling time is included in calculating the delivery estimate (handling time plus carrier's estimate for that class of service to your zipcode) which is what you need to go by for deciding whether that is too long and which eBay goes by to determine when you can file a case (or whatever corporate-speak term they use for that now: it is 1 to 30 days after the estimate) for Item Not Received.
