I'm one of those few people against the 4 / 40 work week. Working a 10 hour day would basically not work with my schedule at all because daycare, my dog, and everything else, work on a normal, 8 hour day. I play in basketball leagues on Tue/Thur and that'd make it impossible for me to make any of the early games. Even if my wife picks up from daycare (which she does now as I do drop-offs), it'd basically make me an absentee father for 4 days a week... My daughter goes to bed at 7PM, and so when I get home at ~6-6:30 that's usually my time to spend with the baby and put her to bed. I do mornings but those are always a bit of a firedrill each day, not really quality time.
I'd love to have a day at home each week to get shit done while my daughter is at daycare. Realistically, I think I'd end up doing freelance or something on the day I have off, and it wouldn't be good for me.