I attempted to go back to my studies (have 4 units left of a Bachelor of Arts degree) this year, but it just didn't happen. DS is 13 months, and when he's awake he's pretty full-on - always busy, always doing something, bringing me books to read, etc - so studying while he was awake wasn't an option. I know myself well enough to know studying of an evening wouldn't work. So, that left DS's day sleeps and weekends when DH was home as the only time I could study.
Of course, right when I tried to start studying was when DS decided to drop to one day sleep... Needless to say, I never really got started with the study and ended up pulling out before the census date (no money lost, no grades lost).

I'd say the younger the bub the easier it would be. Either that, or when they're much older and at school or day care.