I have heard many different hosts say that they have to be at work 3 hours before their shift. They said they have to meet with show planners, writers, vendors and do other show prep. It doesn't matter if it's the same vendors they are with time after time, they go over what is in the show that day, decide who is going to say what, etc.
I remember back when Jane left and started her own website, she had a question section and someone asked about the hours. Jane said even part-time hosts work nearly 40 hours because of prep time, meetings, etc.