Depending on the age, height, trainer level, other skills etc a player will take a certain number of minutes to pop a skill. Lets say for example you were training presure and it was going to take 100 minutes in total (max 48 per week counts) to pop him.
First week he gets 48 minutes, no pop.
Second week he gets 48 minutes, total 96, no pop.
Third week he gets 27 minutes, total is now 123 minutes and he pops. He is now 23 minutes towards his next pop.
Does that help?