Pressure is a very slow training regimen. It's not uncommon to get no pops for two consecutive weeks, if you're training it in two positions. You might want to check this post
(78242.1) to find some precious info on training speed.
As for training minutes, 48+ (which means 48
full minutes... 47'40" for example would be marked as 48 in your "Manage My Team" page) will give your players full training for any given week: any minute above that would be wasted.
You should also consider that training % decreases dramatically for players that get less than 48 minutes. If, for example, one player gets 24 in a week, he will not receive 50% training, but much less than that (let's say 10%, or even less... there's no real consensus on the exact numbers as far as I know).