I think the minimum my nursery does is 1 session (morning/afternoon 3hrs) a week.
Basically the thing to do is start ringing round and getting a feel for the nurseries in your area. There were some I didn't bother considering because of the telephone attitude. Most nurseries will be happy to talk you through your options, probably send you a leaflet which will outline the care provided and the costs and also invite you to have a visit round.
I was very lucky and had such a good gut feeling about the first nursery we went to that we went with them and didn't look anywhere else.
The main thing to look for is people who are keen to ensure that they adapt to you and your baby and they should talk of doing a few trial runs before you start sending your LO there officially.
Lucy's nursery is brilliant, they will cater for any dietary requirements and all they ask you to take is nappies. They completely follow your (and your child's) lead.
Good luck, its not easy sending them to nursery but I can tell you it is 100% the best thing we have ever done for Lucy, she has her own social circle and they have taught and re-affirmed so much that we try to teach her at home.
Oh and if you're not sure about something - bring it up with them. Lucy's nursery isn't perfect but when I've raised an issue they have always taken it on board and learnt from it.
Sorry to over-load you!