I started to have the same problem a few years ago. But after starting to take magnesium tablets every day (I take two), the problem cleared up. Magnesium is an essential mineral for calcium and potassium assimilation. It's involved in nerve and muscle impulses, enzyme reactions,and heart muscle health and more. AND can stimulate the urge to go. It is, by the way, what milk of magnesia is made of.
To get a time idea on timing from taking magnesium until the urge occurs, I take two in the early evening and the urge occurs the next morning. (^_^)