I went back to work when Holly was 3 weeks old (I have my own business so no bugger was paying me maternity leave, nor could anybody else cover me).
It varies from week to week, but she is in nursery for 16 hours, plus I work all day weds whilst she is with daddy and some evenings if things are really busy (like today, I sent my last email at 9pm). All in all, I probably do about 25 hours per week.