I noticed that someone else who did the Miralax/ducolax prep had the same problem I had: they didn't start passing anything until later at night. If you are going that route, I'd suggest starting earlier, maybe around noon, and drink that stuff as fast as possible. Maybe it'll get the train rolling sooner, and you can get some sleep before your procedure.
36 y.o. male
Diagnosed w/ moderate UC in May '06 - currently flaring
Asacol, Florastor, VSL#3, Wellbutrin XL, Prozac, multi-vitamin, Allegra, Lialda, Colocort retention fluid, Prednisone 15mg and tapering down