Any predictable pattern, including when you disengage, is just another feature for the pricing model. If the model learns you reliably leave after 3 hours, it will simply front-load the surge pricing into that initial window.

  Analysis: This user loses disengages during 75% of the
  time and belongs to a group of 5% who do the same. The
  expected revenue for this group over a longer period
  and with multiple users is 24% lower than for the
  average user.

  Action: Since 80% of theirs engagements last for at
  least 12 hours, ads should be shown and prices
  increased only within the first three hours.