Remember that the frequency with which you practice the meditations is much more important than the duration. It's great if you're able to do the full version at least some of the time (last week it was 10 minutes, this week it will be 20 minutes), but as long as you're doing it every day, or almost every day, you'll learn and benefit from this practice regardless of how long you spend doing it. Doing the 5-minute version every day is preferable to doing the 10- or 20-minute version just once or twice during the week.
If you weren't doing it on a regular basis, or even not at all, again try not to be discouraged. Developing a new routine and habit can take time. Here are some things you can try that will make it more likely that in the coming weeks, you'll be able to do the mindfulness practices more often.
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 spend time finding where you've saved the audio files or put your headphones, those are just unnecessary obstacles that make it harder to get started.