Photographer hours, how many?

Hey all, we are currently shopping for a photographer and of course the most important deciding aspect next to Price and how well their work is, is how many hours we would need them for the day. How many hours did you guys plan or are planning for your photographer? I most definitely want them for the getting ready pictures. I'm planning for a 4 oclock ceremony, with a cocktail hour for at most an hour for photos with family. I don't feel like the photographer will need to be there the whole night because I haven't really decided on if we will be having a major exit. Just looking for some insight from other fellow brides. TIA