I haven't set up anything yet through the new 'available now' feature, but have been monitoring it and hope to utilize it regularly, since it's usually difficult for me to schedule in advance.
One big plus I see is that it at least indicates the advertiser is in town and currently seeking appointments. With so many providers who travel frequently, that's nice. Several times, I have clicked on a profile that appeals to me, only to find that the subject is gone for the week.
A nice feature I just noticed is that if you see an ad you like, but the advertiser is not available when you are, you can subscribe to that provider and get an email notification from P411 each time she places an ad.