I would say offer a 30 minute appointment. A lot of guys now go for a half hour with a new lady to see if they get along before booking anything longer. In order to try and hang on to some of the hour bookings, you might consider adjusting your prices so that an hour seems like a much better deal? It's up to you whether you make your 30 minute quite expensive or your hour a little cheaper, but don't fiddle with the prices too much, as it makes clients suspicious that you're not busy or you're not very professional (and they may think they can haggle! L'horror!). I adjusted mine a bit when I first started and haven't touched them since.
It does take time to get busy these days, I presume because guys are less willing to take risks on new girls if they've got less cash to lose on girls who may or may not be good (I'm sure you're awesome, but they don't know that if you haven't got much feedback
). Personally I didn't see the 'new girl' rush that everyone talks about when I started working before xmas last year, but once I put together a really polished profile on AW and a good website, and splashed out ?350 on some professional photos, and had a review or two, things began to get so busy that I'm now able to really choose my clients carefully and I enjoy my work a lot more as a result. Despite this, even once you're a bit more established you will still have quiet times. I had a dead week, followed by a week where the phone rang off the hook (and naturally, I was rolling around clutching my stomach and trying to put as many tampons as possible inside myself ... sod's law.)
I began with almost nothing, so I can sympathise if you're reading this advice and thinking 'I can't afford expensive photos or a fancy website' ... The photos may have to wait (although, as someone's already said, you can start off with some taken by an amateur until you've built up some capital) but a website doesn't cost much if you write your own content. Emily and Ian, mods on the board here, made mine and it's really excellent and was incredibly inexpensive.
Don't lose heart. If you want any more advice or maybe another pair of eyes to take a glance over an AW profile or proto-website, just PM me. I'm trying not to blow my own trumpet here, but I'm pretty sure my shiny AW profile and my chirpy website are the main reasons I'm busy.