miralax works in like 8 to 12 hours. UNLESS, you are doing the pre prep challenge for a colonoscopy. They have you take a full dose every 15 to 30 minutes till a 2 week supply is gone. You start pooping in about 2 hours, but its not something you want to happen unless you are doing the challenge.

Take a big full dose, follow it with plenty of liquid thru the day, and by the morn, you should be ...um...dropping the kids off at the pool as my son says! I always hated that saying.

good luck.