From a photographer's point of view, the longer the better...more time means more photo opportunities.
But to be more objective, i think the "getting ready" shots are great to have, of course the ceremony and a little session with the bride and groom...Then it is about getting the fun moments between family and friends, for my wedding, I was glad to have a photographer until the end of the night to document people getting crazy and having fun on the dance floor after a few drinks...