I always felt like you had to have a good night's sleep to dose dope after buprenorphine, and that is more important than the # of hours that have passed. This is my own experience. It never seemed to make sense to me either. If I dosed 2mg suboxone at 8AM, then I wouldn't be able to get high on dope all day, and I would have to sleep for a solid 5+ hours before waking up and being good to feel some dope. So, in that case, its 24 hours.
However, if I dosed 2mg suboxone at 3PM, I would still be OK to do dope and feel high at 8AM the next morning provided I got my sleep, only being 17 hours later.
But going back to the first case, dosing at 8AM, and then waiting 17 hours without sleeping, trying to get high off a shot of dope at midnight or 1AM, being 16,17 hours later I still couldn't feel the dope, so I assume the bupe was still blocking the dope.
There's something about sleep that seems to let any opiates in my body fall off the receptors. It's weird.