unit – How to trigger periodically in the unrolled time a script?

my simple goal:

instead of pressing a key, this triggers a script like this:

if (Input.GetKeyDown (KeyCode.Q)) {// script}

a specific moment and chosen (for example every 5 seconds), after having introduced into void Start () {time + = Time.deltaTime} the time began at the beginning of the game, triggers the script.

What should I put in place of Input.GetKeyDown (KeyCode.Q)?