For some events the tickets are not sent to the original purchaser until just before the event (usually about three days prior to the event), so the tickets are uploaded a day or two the event.
In another scenario, most sellers want to give themselves the most time possible to fulfill the sale because if the seller puts a delivery day of May 1st, for example, and the tickets aren't released until May 10th, the buyer can cancel the order even if the event isnt until May 27th. In this situation, the seller would have to pay a penalty of 40% of the sales price, or the cost to replace the tickets for the buyer, whichever is greater.
Most likely the tickets will be uploaded and you'll have absolutely no issues. However, if the tickets are not uploaded by the end of the delivery date promised, reach out to StubHub customer service at 866-788-2482. They can reach out to the seller and see what is going on. If the seller cannot fulfill the order, Stubhub will replace your tickets with similar seats, or better seats, at no cost to you... Alternatively, you have the option to cancel the order at that point and get a refund also.
Like I mentioned, you'll likely have no issues at all as the majority of transaction on StubHub complete flawlessly!
Enjoy your event!