interaction design – What is a good multipress timeout value for pressing a hardware button?

I am looking for a value to specify as a maximum time between presses for it to count as a multi-press when pressing an hardware button on e.g. a mobile phone. An example would be to execute an action by pressing twice (or more) on the home button.

Of course the optimal value will differ a lot depending on the user, but I find the value commonly used for mouse clicks being 500ms, and I think 300ms is sometimes used for double tapping on a touch screen. But what about a HW button on e.g phone?