First identify the shot. If it was a heart/lung shot, you can go in after 20 minutes. If it was a gut shot you'll wanna wait several hours. If the deer is down where you shot it, you probably don't have to wait long, just make sure you approach it carefully with a loaded gun.

You are very lucky if you've never lost a deer that you approached right away. You should read the book "Finding Wounded Deer". It is brilliant and should answer any questions you have.