[HardStarboard]

>>>How many seconds did he have, assuming he was going at least 40 mph?

If he dropped 600', it would take the same number of seconds at 40mph off the cliff as it would at 65mph or 105mph off the cliff.

The acceleration [downward] of gravity is a constant 32ft/sec/sec.

Assuming he drove off the cliff exactly horizontally the equation is D=1/2 at², where D = 600', and a=32'/sec/sec. Solving for t [time] you get 6.12 seconds - far to long to contemplate your mistake.

[Lonesome in Massachussets]

You forgot to account for lift. The faster you go, the longer the tailfins hold you up ;)