Keeping the ceremony on time is very important. You have quests waiting and they may have plans later. There are also the vendors. You have them for a specfic time frame most will charge extra for time used or at the end of that time will leave due to other engagments that they have. That is not fair to you to have vendors leave because of a late starting time.
With all this being said, have fun on your special day, make it enjoyable for everyone and most of all enjoy the bliss of your marriage from this day forward and forever and ever.
Blessings on you all have a good July 4th.