Thanks for all the replies really helpful.
Ms2 doesn't nap (except on me now or in car) so couldn't count on naptimes. I go to bed about 10 so can't see late night as much of an option. Maybe early mornings when she finally gets her own bed. I think I do need to keep researching what I can study that has decent long term job prospects. If I'll need to be prepared to use every free moment I need to be sure the study time won't be wasted!