If you get to Sunday night and still haven't had a good BM, then I suggest that you purchase an insurance policy that will guarantee results before bedtime, and insure a comfortable Monday with no surprises.
The insurance policy is simply an old fashioned enema bag. A cleansing enema at bedtime should produce immediate results that will likely suffice to get you through the next day without having to move your bowels at an unpredictable moment.
If you are not familiar with how to give yourself an enema, the following links will be helpful:
For the longer term you may wish to consider professional colon hydrotherapy (colonics). See the Enema, Colon Hydrotherapy, Colema, Colonics, coffee enema Forum for more information.