YES do it @B2B25 I have been to two 12 hour marathon weddings at a special venue in 2 years (both weddings cost £20K+.) And both of them were such a fucking ordeal. This is pretty much how they both went...
We had to be at the venue (20 and 25 miles away) for midday, so had to leave at 11am, the 15 minute ceremony was 1pm, and the one and a half hour reception/wedding breakfast was at 3-pm, then the 'night do' started at 7.30pm!
So first of all, we had a gap of nearly 2 hours between the end of the ceremony and the reception, (the bride and groom were away nearly an hour having photos taken, and then they came back and lots of family/group photos were taken.) And then after the reception (3pm to 4.30pm,) we had THREE HOURS between the end of the reception, and the night do.'
So, (including the travel time,) we had a 12 to 12 and a half hour marathon by the time we got home at 11.30pm. We were bored shitless, and tired, and weary, (because of spending so much of the bloody day hanging around!) and just felt so fatigued by the time we left! There were plenty of seats around, and a bar open, but it was still soooooo tedious! 
(We had to be there an hour before the ceremony for pre-wedding photos, and to be seated ...)
I went to a 4.30pm wedding in mid December, and OMG it was soooooooooo much better! Pre wedding photos, (half hour,) ceremony, (half hour,) bride and groom went for photos alone for 40 minutes, then they came back, and we all went straight into the reception. It lasted an hour, and then it was the night do at 7pm! Amazing! This 4.30pm wedding cost less than £5K too.
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