ANSWER

41 minutes

84 feet for 18 minutes -> Group F
Group F on the surface for 1:30 ->D
Group D at 52 feet  max time -> 26 (so 15 minutes is o.k.).  Residual Nitrogen time is 24 minutes.  Add RNT (residual nitrogen time) to ABT (actual bottom time) of 15 to get 39 minutes.

52 feet for 39 minutes ->G
G out for 2 hours ->D;    D at 44 feet can stay 41 minutes (29 minutes RNT)

 

Text Box: 18 min Text Box: 18 min Text Box: 41 min