Good to see that someone took effort to post this topic. ;)
Though, I don`t think that the progress is the problem, since the progress time with the NPC at Charge Island takes 50 and it still gains 600$.
I think that the missions should be removed or reworked to avoid that payment problem.
If my theory above is wrong, then I support the idea to increase progress time.
EDIT: We could replace the mission with a new one, which would be epic. For example;
"Dispatch: Happiness Island statue is breaking down"
You`ll need an EMS boat (which WheelRider probably can make) or the old helicopter back.
Fireman will need to fix the statue that is falling down and medics will take care of the NPC`s.