Lets be reasonable about it. Considering the tremendous amount of skill & effort that us unselfish chaps put into reverse oral, surely some form of discount should be applied, either financial or thru extra time added on.
Dubiously, there must be something wrong with your RO technique Mr. H. For there is always a juicy reward when RO is done with expertise ( The lady's sigh ,the little pelvic thrust fom the lady and her hands pushing your face deeper).
Your reward is that you have given some satisfaction to her for the pleasure she has given you.
I am paid for time, and if you choose to spend that time talking about chess or snorkel deep in my poon tang, then that's your prerogative. To a greater or lesser extent it is up to the client to use the time wisely.