Its been done and is still being done. That is one helluva lot of work to get done in a short period of time. The progress tests require you to have read 90% of the notes to pass, unless you have previous aviation knowledge to JAR level (unlikely unless you're a total anorak!) No brush up until all progress tests submitted. Thats assuming you don't cheat
Mod one is a lot more conceptual IMHO. So it takes longer and requires you to brush off those old trigonometry / algebra notes. Mod 2 is more "content learning" based, although the electrical theory is trivial to the extreme a la JAR....
I would say a min of 6 months for both mods if you're committed to it. If you are very sharp and can learn very quickly, then no doubt less.