If you are having a great time with a provider and you look at the clock and notice you are running out of time, is there a best way to see if extending the time is possible?  

I realize we are not to talk about money, so how do I get around this issue?

Start by asking if she's available, and willing to extend the date. You're not to talk about money in phone calls, messages, emails, etc., but if she's available and willing, you can ask what it will take to extend the date for the length you want.

It's good to keep that info handy just in case, as well as some extra $$ in your pocket.

To be discreet, you can get up and say you need to use the John and give her a wink.  Then leave the $$ on the counter in there.

She'll know exactly what is going on.

if you are already very in-session then asking to extend and how much it would be is OKAY.  Don't worry about the taboos at that point and be forward.  Just remember to ask "can I extend?" and not "when is your next client?" - one is perfect, the other not so appropriate.