After awhile you will know when it works. If you do it at night usually starts the next morning.
This morning I had to go to my workout and had overeaten the last 2 days, so I took 3 pills at lunchtime yesterday so I got emptied late in the evening and the last time this morning.
If you know you go out the next morning don't take it the evening before, after you come back and you are going to be home the rest of the day take it then. We are having company to-morrow and I am going to take 3 pills (that seems to work for me, very seldom I use 4 pills) to-day after lunch.