Double-tap or two single-taps?

Question

What is the time limit for two taps to be considered a double-tap, on the iPhone OS?

// Edit: Why is this important?

In order to handle single-tap and double-tap

Answer 1

I don't believe there is a default time-limit - it's whatever "feels" right when you try it out. Apple has an example here, where they don't specify a specific time either.