Not sure what you mean by this.Yes, worked rather hard at it. As tursiops said, it isn't linear with depth.
I came up with this for your first hard deco in minutes: divide depth squared (in feet) into 222,222. Compare that to Navy Air Tables.
Cutting to the chase, I came up with something for a multilevel dive that probably wouldn't kill me, but I wouldn't trust it either. The more I learn about deco, the less I know to be true.
By "first hard deco in minutes" do you mean an NDL time for some depth?
Do your really mean 222.222/D**2, or do you maybe mean D**2/222.222? the first one, which is what you wrote, would give 0.06 for 60 ft. What does this mean? At least the inverse gives 16.2, which might mean something....but what?
And you really mean 222.222, not just 222?
The old Depth (ft) plus Time (mins) = 120 is perfect for the (old) Navy tables, between 60 and 90 ft. Above 60 ft you get much more time than simply D+T=120, and below 90 ft you get less time than D+T=120.