Doing 14 minutes is still better than 0 minutes. The difference between 0 and 10 minutes is likely higher than the difference between 10 and 20 minutes.
Start easy. Don't put the goal too high. Don't have a defeatist or perfectionist attitude (relapse is a natural part of changing a habit). If you have to stop earlier because your body tells you so, accept that, and retry the next day. Once you start doing it regularly you'll notice the difference. It will go easier. Especially in the start. Later on, you can increase your limit, aiming higher, until you meet your goal.
If you're doing it regularly and then end up skipping it once, the effect of that is negligible (unless you're pushing it but you're not an athlete, are you?). Just like if you're eating usually healthy and not too much the impact of that Christmas dinner is minimal. Just like with brushing your teeth if you brush them twice a day and end up skipping it once, it isn't a big deal but if you regularly skip and neglect your teeth there will be more of an impact.
Realizing that makes say losing weight, getting fit, and maintaining dental hygiene easier. Heck, it makes life in general easier as well since it is never too late to start compared to going on with the bad habit. I loved your GP comment as well, it makes so much sense, and has a similar soothing effect. Thank you for making that point.