You are notified as soon as the auction is over. Most sellers prefer that you pay asap as ebay does charge the seller final value fees as soon as the auction has ended. ebay does allow a 4 day grace period before the seller can file for an unpaid item...then the seller has to wait 4 more days before they can get their fees back and relist their item. At that point, the buyer has an unpaid item strike. Many sellers block buyers who have 2 or more or those strikes.
Your seller can agree to wait until you come back but to be honest, I wouldn't be crazy about waiting that long for a brand new ebay buyer as there is no guarantee that they will pay. If you don't hear back from the seller and you are still the high bidder, you might want to retract your bid.