I was aiming to complete 2 modules of a diploma by correspondence before DD was born but didn't achieve much in my 1 month off work before she arrived. I ended up doing the self study, 2 major assignments and 2 exams after she was born.

I found that it was way easier to do stuff when she was a newborn. She slept for longer, laid on the floor in the spot where I left her for tummy time and it was easy for DP to look after her and just bring her to me for feeds when I was working to a deadline.

So my advice would be the earlier the better. HTH