The distance learning time is obviously decided by the individual student, and his or her ability. Those who have posted here have been reasonably quick, others do take longer. I know FFF for one is bright and able. In any case most people who choose distance learning are somewhat academic, whereas the classroom can have a complete spectrum.
The classroom time for a full-time course is about 650 hours. This is also the recommended minimum for distance learning, with minimum 65 hours classroom (all courses I know, including the one I will be teaching, are around 120 hours in the classroom).
I learn in the same way as you, by understanding but hating rote learning. I sat all the exams in 2000, from a full-time course. I found most of the subjects relatively easy, achieving good grades with, to be frank, less work than recommended by the school of an evening (I am lazy). However I still did a fair amount, and a lot was down to previous experience (a numerate degree and previous flight groundschool) and academic aptitude and I still struggled with a few subjects.
You will find there is some "bulk learning" required, which was where I struggled, especially in Law, part of Systems and in Ops Procedures as well as the climatology section of Met. For the last of these I developed the technique of reading for ten minutes in bed every evening. This not only got me a very high mark but solved my sleep problem (I am not kidding, it is great for this. It's so boring).
Best of luck!
Send Clowns
Gen Nav / Flt Plng instructor
BCFT