[Moral Hazard]

I'm quite familiar with the concept of diminishing returns, but the original quastion did not include an real-world factors that might affect the time.

[Fierce Allegiance]

OK, but I would go with the 3.5 minutes. I like nice round accurate numbers over multi-decimaled precise numbers. Besides, if you want to get mathematically technical, there is only one significant digit in each number, both times being integers, so any precision to the right of the decimal point is bogus.