I had lunch with a fried who told me about a wedding she and her family (including 2 little kids) attended earlier this summer. It was held outdoors on a sunny (and hot) day and the ceremony was over an hour long.
While some religious ceremonies can last longer than 20-30 minutes it is important to think about your guests when planning it. I'm not talking about editing the ceremony itself, but if you are getting married on a summer day you should provide seating, shade and cool beverages for your guests.
I remember a wedding in Puerto Rico I worked when I was at Martha Stewart Weddings and it was hot as hell and the ceremony was held on a putting green so the editors arranged for iced beverages to be passed before the ceremony started and parisols were available for the guests too.
The wedding my friend attended did not offer iced beverages or cover from the hot sun. There were a number of older guests as well as kids at the wedding who became very uncomfortable as the ceremony went on (and on).
If you're planning to get married outdoors on what could possibly be a hot day, think about having a tent available to shade your guests or if the cermeony won't be too long offer fans and parisols. I'm sure you've seen fans with the program printed on it so you can combine two details into one.
Talk to your caterer about offering passed beverages - alcoholic or not - before the ceremony begins or having a bar next to the ceremony site for guests to grab a drink before taking their seats. And don't forget my post last week about seating. Always have seats available for elder, disabled and pregnant guests and of course kids.