Remember that it's much more important to practice the meditations on a regular basis, regardless of for how long, than it is to do a longer meditation less frequently. If you're doing the meditations every day, or almost every day, you'll learn and benefit from this practice regardless of the duration of your meditation.
If you're having difficulty making the time to meditate:
Make sure you have everything you need to do the meditation ready to go in advance. If you need to go searching for a cushion or mat, or search to find where you've saved the mp3, those are just more obstacles that will make it harder to get started.
At this point of the program, often people experience a bit of a letdown. At first the meditations are new and it can be easier to motivate yourself to do them because of the novelty, but by now it can be a little more difficult to bring yourself to sit down and meditate. And if that's the case, don’t let yourself become too discouraged as this is fairly common, but also remember that the more effort you put into doing the meditations, the more you’ll get out of this course.
Do your best to devote at least 10 minutes a day to meditating, but even 5 minutes is so much better than nothing, as consistent practice is much more important than the duration. Everyone can find 5 minutes in their day to meditate if they make it a priority, and once you start doing the meditations on a regular basis, and especially if you do them at the same time every day, it becomes a habit and part of your daily routine.