That is my beef with boarding at a vet's office. My experience has been very typical to yours.
They don't take them out to pee/poo very often even when they are there.
Then on weekends they only take them out twice---once in the a.m. and once late afternoon.
My guess would be that the dogs are supposed to hold their urine from around 5:30 in the eve. until 7/8 in the morning. That is absolutely crazy!
We're going to TX April 5-6 to see our son and his family. Don't want to take all four furbabies along and burden my DIL. I have to keep them in ex-pens and Snowboy, the Pommie, would howl up a storm. He's such a mama's baby; follows me everywhere, and sleeps against me at night. I would like to find a safe place for my Pommie and 1 1/2 yr. old Yorkie, but that could be a problem. I
am not going to board them at the vet. There is a girl in town who will feed and take the dogs out. I've used her before but I figured out that she does not play with my animals at all. Returning from one trip, I found the cat's toys exactly where they were when we left.
What I would like to do is stay home with my furbabies and just let my husband and our daughter go down to TX. Wouldn't that cause an uproar!