Really? What is it based on?
There is NO set schedule and I would not recommend against soaking your animal unless it's ABSOLUTELY necessary. There is not need to put an BP though unnecessary stress because the animal does not defecate after 3 meals.
Defecation varies from one animal to another there are various factors that come into play as well such as: age of the animal, feeding size and frequency etc
Younger individuals utilize most of the prey for their growth therefore there might not be much waste etc
Ultimately he will go when ready.
Now if the animal was impacted this would be different and soaking would be recommended, but unless your snake as a bulge near the vent area that does not seem to go away I would not worry about it.