Late night and short notice sessions are available with many ladies here.
Spontaneous visits can be very fun! But calling your references late night isn't so fun. Sometimes we can't reach her and it can take a day or more to recieve a response.
Try this: Ask the lady you are interested in (or in lust with) if she will pre-screen you without scheduling a date yet. This gives her time to get a gold star from your references. Then you are good to go when the late night, last minute *urges* strike!