I am not able to sit three hours without taking a short walk break. But I am much older than you, I would guess. The ol' knees to be straightened and worked a bit from time to time by walking.
I bet your horses would have appreciated it you'd gotten down off them for that long wait for your friends. even a well-fitted saddle can cut off the surface blood flow to the skin right under the tree, so giving the horse's back some time without it being weighted is a courtesy you can give your horse from time to time.