How sooon does miralax (polyethylene glycol) make you have to go?

Hours to days. Miralax (polyethylene glycol) works by absorbing water from the colon allowing it to move easier through the bowel and pass the stool. It probably needs to be taken daily to be effective . It is not like milk of magnesia or citrate of mnagnesia, which should only take few hours to be effective.
Usually within 12 hr. May need to take more than one dose. Need to drink lots of water. At least 6 glasses (8oz) a day minimum.
Dose-dependent. The more MiraLAX (polyethylene glycol) you take the faster it works. As a once over-the-counter dosed laxative you may not see results for 3-4 days, but as a multi-dosed colonoscopy preparation (when used under doctor's advice) expect laxation within hours. As with any laxative however understand its mechanism of action, its risks, & treatment goals & make sure you are not missing obstruction, dysmotility, inflammation.
Dose-dependent. The more MiraLAX (polyethylene glycol) you take the faster it works. As a once over-the-counter dosed laxative you may not see results for 3-4 days, but as a multi-dosed colonoscopy preparation (when used under doctor's advice) expect laxation within hours. As with any laxative however understand its mechanism of action, its risks, & treatment goals & make sure you are not missing obstruction, dysmotility, inflammation.