I completed my distance learning ATPL last month with NAC.
Notes were not very good (I used OAT ones to study) but nice and helpful instructors.
I took five months to prepare my module one (with some holidays in the middle) and three months to go through module two. I used to study really a lot (at least 7-8 hours during weekdays) with poor social life; specially because you have to prepare everything by your own (a good background is essential).
However, I passed all first time with a very good pass rate...that means: it is absolutely possible to do so, don't worry!!
All the best