I prefer bookings of two hours or more, I don't feel as rushed or under pressure, even with new clients. But I tend to get them to be as detailed as possible in what they want before we meet. I don't offer bookings under an hour anymore, I found my clients were consistently over running.
It does help that most of my clients want multiple services, role play, bdsm, using toys on me, and RO. We just chatter while they catch their breaths between rounds. Helps as well that most put me on top, so I can control the depth and pace and really tease them for quite a while. Give them a show and get to enjoy myself.
Think my longest booking was 14 hours, that was a bit of a mission, but anything upwards of 6 I can handle pretty easy.