Unless a restaurant has multiple meal services and needs to turn over your table, you're under no obligation to pay immediately when you receive the bill. That said, why wait an eternity? The quicker you pay, the less time you have to worry about getting your server's attention when you are ready to leave. The worst is when diners do this: "Not paying your bill for 45 minutes after I deliver the check and then getting mad that you couldn’t find me the second that you wanted to pay, even though I’ve been circling your table like a shark."