How do you plan for a dive when you have already built up an amount of nitrogen and it has not left your body through respiration yet? Your dive computer will take this into account when you start your dive planning. Your NDL times will be reduced. This will determine how you plan the dive. Your gas consumption will be the same, so you can work on the same average times.
The dive computer’s reduced NDL times for your dive will most likely be the limiting factor rather than your gas consumption. It is important to know that as you stay out of the water, you are off gassing and will be increasing your NDL. This takes some time, and again, the dive computer is able to calculate your NDL.