Before I get to your question, I would just like to say that I hope you are doing a show, or a photo shoot, and not just doing it to look good at the beach or something, (my opinion).
Anyway, we need to know your water/carb intake before any specifics can be given.
What I do before my shows:
2 gal H2O for 4 days.
On 5th day, (which was day before pre-judging) cut water except for sipping.
8pm, 40mg Injectable Lasix (I do not recommend oral, because they are harder to predict). Within approximately 120 minutes, it has taken most all of the effect it is going to.
I never needed anymore, and I had no problems with cramping doing it this way.
Hope it helps.