First off congratulations on being a father!
I was in a similar boat, father of 2 (2 year old and a 3 month old), work in public accounting, with greyer hairs being 33.
My study time started around 3:15 am until about 5 am, would get my daughter ready for school/daycare, get to work about an hour early and get in another hour (plus an additional 10 or 15 minutes). I would wake up at 3 religiously everyday, hit the coffee-maker (coffee was ready to be brewed already) and get on it. I couldn't do the after work studying, I never studied at night through any of the 4, not once. The morning was quiet, everyone was sleeping and my brain wasn't tired from work.
I wasn't getting the most sleep in the world, usually in bed by 10:30/10:45 pm (not out of luxury – wife and I need a little time to breathe and for ourselves after the kids are asleep) so I would shoot for 4 to 4 and a half hours, but probably overloaded a bit on the caffeine to get me going. Weekends I woke up around 4 am since my daughter would wake up around 6:30 – 7 am and I love my weekend mornings with her and the family. I studied weekend afternoons sporadically, depending on how much we had going on but a lot of times an hour if that.
I made up for it but squeezing in MCQs during “lunch”. Although I wasn't putting in an insane amount of hours during the week, I think I spread the material out enough that I retained it (12 weeks for FAR, 7 weeks for AUD, 6 – 7 weeks for BEC, 9- 10 weeks for REG). I took a risk but figured to pour in enough time to get each one done the first attempt and it worked. Also, I found that my best learning happened during my review stages, so I would rush through my first go-around with the material, since for whatever reason whatever didn't stick would click much easier on the review even if it was brief.
Of course some mornings were tough, my head would literally slam onto my mac and I'd barely get a lecture in but I wouldn't get discouraged and pushed on. REG was my last and had the least amount of time (second daughter was born in April + busy season) but I hated studying so it pushed me.
Best of luck to you, once you find your groove you will knock them down.