Of course, for every practitioner learning a new practice, that is the top concern, about how to keep up the practice regularly!
The mind will throw up a variety of reasons as to why the daily practice cannot happen ranging from family to work to illness to social commitments and many more. At a very basic level, it all comes down to how much you value the practices. If you value this above everything else, you can easily make it a priority and find a way to fit it into any schedule.
The reason why we always recommend the 21 day program over any other program is because it gives you a better chance to notice this value that can be easily missed in a shorter program where physical exhaustion overpowers any desire to improve and one could easily just give up.
If you are not experiencing the value strongly enough, again it will be easy to give up the practise and your mind will support your decision with plenty of good logical reasons to do so.
So one simple way to ensure you don't miss it is to just deepen your involvement each time you practice. Work up your intensity in the asanas. Reduce any distractions in your mind and body. Deepen your focus with every little thing that you are doing in class or a practise session, whether it is watching a demo or listening to a talk or sitting with your eyes closed.
Also, why reduce yoga to just a two hours a day 'practice'. See how you can sustain the same level of awareness and intensity throughout your day. Whether in a meeting at work or while having dinner with friends, every moment can become an opportunity for you to grow within yourself and inspire those around you.
As long as you can sustain this, you should be fine. You won't have any trouble keeping up your Sadhana.