My DS (pfb) has recently started going to nursery 1day a week 8-4.
He's 18m old now, I went back to work when he was 9m old and he was cared for by a family member but that didn't work out so I chose a nursery instead.
Nursery were really good, and obviously aware that 1day per week children do take slightly longer to settle, they let me take him for visits 2/3 times a week for the first few weeks, then leave him for 1hr, 1/2 a day etc to begin with.
He's been there 5weeks now, I'm confident that he's happy at the nursery, as when I collect him he drags me around gibbering and showing me stuff, he will eat/drink/sleep at nursery and when asked 'where are you going tomorrow?' he'll answer 'skooool'!!
He does however get a bit upset when he's left in a morning, tho staff advise that this is normal and he soon settles, he also can get upset throughout the day if something happens but again I'm advised that he soon comes round and can be soothed and easily distracted.
I'd advise you to go for it, it's is a bit unsettling for everyone at first, but we won't be the first to do 1day a week and we won't be the last either! 