Fleet Enema is a saline laxative enema, which works by pulling water from the body into the bowel, and helps soften the stool to produce a bowel movement.
Usually the urge of going toilet is around 2-5 minutes. If it does not produce motion, in this duration means, either the stools are two hard or the rectum is empty.
You can read about it here
Please feel free, if you have further questions.