Schedule the Photographs
Your photographer will have a guide list of essential snaps. Great, look at it and turn it upside down.
Getting all the group shots in first will mean elderly people are there (and not just nipped off to the loo) they can do it whilst looking good, then disappear and find a shady seat.
Then get the groomsmen shots out of the way before the ties start getting loosened and the jackets start coming off, then the Bridesmaids and finish with the Happy couple, in peace, with everyone else shoved into the shade. Not only will this reduce the overall time spend herding an ever growing crowd of people, it means you can make your entrance, possibly via a quiet cool drink and a cold face cloth.