If you have been fasting today exactly (to letter!) how it is described in Clarks recipy and if tomorrow untill around lunch time you are around comfortable toilet, you can do it even today. It may make you feel very tired tomorrow, so you decide if you can do it.
I am sure your pain will be lessened after the flush, surely you will not feel worse then you do. If the pain persisits you can flush again using your free Saturday. But I hope you will fix your problem with this one flush.