If you're planning on having your ceremony and reception in the same place, you're doing a great thing for guests, since there will be no gap between the vows and cocktail hour. One will flow seamlessly into the other. But if this isn't your particular scenario, read on for some pointers on long breaks and guest comfort.
A break of 60 to 90 minutes is fine.
If you're moving onto a different spot in town for the party, having an hour between the end of the ceremony and the start of the reception is fine—it'll give everyone time to leisurely make their way to the second venue, or to even go home or to their hotel room for a short break. Anything longer and guests will start getting antsy, but it's impossible to avoid in some instances (like when you're hosting a church ceremony that can only happen at 12 noon).
Provide ideas and activities if a long break is inevitable.
Think about what guests will do if there's a multihour gap. Maybe it's happened to you at a friend's wedding. The wedding was a three-hour drive from your home. You arrived on time for the 3:00 p.m. ceremony. When it was over, you checked the time: 3:25. You looked at the invitation: The reception wouldn't start until 7:00 p.m. What are you supposed to do when you've got several hours to kill in an unfamiliar town? Consider hiring a bus to take guests around town (or a nearby town) to see the sights. Or come up with a list of fun activities that people can do in dress clothes (visiting an aquarium rather than renting dirt bikes).
Ask local loved ones for help.
If many of your guests are local, ask if any of them would be willing to host an informal post-ceremony/pre-reception get-together so out-of-towners will have some place to go. Light snacks and beverages would be perfect—anything more would be competing with the reception!