In comparison to your situation I had 6 weeks to prepare for REG on 07/19 (my fault for taking time off after FAR). I can't study at all at work so 45 hours + 8 hours of commute time. That leaves me with only about 25-30 hours per week to study because I still have to make time for the kiddos. I'm not saying I'm in great shape, but I think I have a good chance of passing with 150-180 hours of study. If you can study for 8 hours a day, 6-7 days a week then you'll get more study time than I am in the four weeks you'll have from FAR to REG. Discipline is the key. I really need to stay off this forum, but it does motivate me to keep going. If you think you can discipline yourself enough then I would focus on FAR for the next 3 weeks and start studying for REG the day after you take FAR. If you start splitting time now it may hurt you for FAR. I dual studied for BEC and my first AUD take and I failed one/passed one. Dual studying is hard and it may just confuse you more. However, if you feel the need to do that then I suggest you studying tax because it has more overlap with FAR than the b-law stuff does.
CPA Exam - Finally DONE (November 2014)
BEC (08/10/13) 80
AUD (08/24/13) 65 (11/13/13) 85
FAR (04/12/14) 81
REG (07/19/14) 69 (11/29/14) 87!!