I don't think your pool will be ready by Monday. I helped my friend switch 2 years ago with about 37,000 gals - it took about 4 days till the water was holding any amount of chlorine. You will have to be very consistant, and you will have to backwash and vacuum to waste often. I would start the switch anyway, because the water you have now doesn't sound safe to swim in now. Good luck, you will be soooo happy you did it.