Speaking from the vantage point of my OWN "hyperactive kidneys/low-capacity bladder": I can go to bed at night and not wake up until morning (well, I *used* to
), but during the day I can't pass a potty without having the urge to use it.
At night, when it's quiet, and I'M quiet, there is no "urge". But during the day, when I'm up and moving around, there are different pressures put on my bladder. Moving around uses different muscles which then exert their influence. There is also gravity to factor into equation. I would imagine that it's the same for a dog ...
Think about it: how many times a DAY do you need to use the bathroom versus how many times at NIGHT?