In my own personal experience with water loading, holding your urine from 7am past 7:15am would be an accomplishment in itself. Effective water loading = having the NEED to piss every 15 minutes or so for a couple of hours after your last drink, at least for me it does. I have almost pissed myself a couple of times on the way to and from tests having to stop at multiple fast food restaurants along the way. I wish you luck. If you were able to hold it a couple of hours, the efficacy of the water loading process, in my professional opinion, would be diminished. How much? It depends on your own physiology. Keep the pipes flowing.