At the moment I'm working 38.5 hrs around all 7 days of the week. I'm also looking after our 9 month old. He's is not in nursery for several reasons (one being cost, it would be more cost efficient and better all-round for me to drop hours if really needed).
Over the past few weeks I've seen that it's reasonable to do 6 hours a day but I certainly need a rest day as the one week I didn't do it I felt completely overwhelmed.
It doesn't help that we go to bed fairly early (around 10) so I try not to work in the evenings as it eats away our time together.
I manage about 6 hours starting just before 8 and finishing around 6. Which isn't that bad but of the baby has a bad day, need to go the shop or something unplanned happens it wrecks the "balance" for the rest of the week.