Colonoscopy and picolax not working

I am booked in for a colonoscopy and an endoscopy tomorrow afternoon and was told to take a sachet of picolax at 3 pm today. It's now 4 hours and still no bowl action and no feeling like it's coming. I'm also meant to drink another sachet tomorrow morning at 7. I have to be at the hospital at 12 which means I need to leave home at 11 am. I'm worried I will need to go in the car on the way and that nothings going to happen tonight. Has anyone ever not had the Picolax work and how long has it taken for you?