I would forget to study some days, and had to find ways to make myself remember. So, I think having notifications from a mobile app would really help. Also, I got completely off my schedule that I created early on, so I think having a proactive scheduler would be helpful. In my case, I started an ambitious plan in January, and barely touched it until May. So, since the scheduler didn't keep track of the days passing, I've been doing content from February, March, and April. What comes to my mind is a Duolingo model; keeping track of the days, having notifications based on missed days, and constantly adjusting to the days and keeping up with the calendar--o, not having a specific calendar-based model at all, but simply having a week-by-week model.