Lets say that the chances of pregnancy taking it strictly are 1% - taking it a little off each night will only increase it something like a thousandth of a percent (1.001%). This behavior can lead to missing doses, unless this is part of something that you always do like just before bedtime. Mind a few hours either way is not a problem, its when you are taking pills way too soon (16 hours or less for 24 hour medications) that your levels of drugs can be 'stacked' meaning you have more of the active drug in your system then prescribed. If you should have to take other medication I would strongly suggest going by a clock. Especially medication that needs to be taken 2 times or more per day. Yasmin is a 'levels' type of drug that you reach a certain therapeutic level within a week or so of taking it, this means it takes a while for the levels to drop (a few days, a couple of weeks). Most drugs will stay in your system longer than specified for time of dosing, however after that time is up the level of the drug begins to decrease. Depending on its solubility it can be as little as a few hours. Yasmin is one of those that the longer you take it the more time you will need to get it out of your system. Thus it is possible that when you do choose to have a child you have to be off yasmin totally for like three months.