Yes, I would wait until Monday. A new relationship is not really the place for a first time bowl cleanse. I have not used the P&B shakes, but I do know that men don't like to think of women in that way - you know the sort who poo and have flatulence :)
Now for too much information : I didn't fart around my boyfriend for the first four months of us dating, until one gassy day, when I just had to. I apologized after I farted and he said "don't worry it's ok, just never do it again :)" I still tease him about that to this day, because he was serious!
(most) Men have an unrealistic impression that because women are "the fairer sex" that they do not have the same body functions/needs. My suggestion is not to pop that little bubble of illusion for now. Let him see you through stary eyes, and then when you truly know each other let one rip :)
Good luck on the new relationship!