Jump, fall, and after determined time it's able to jump again.

You should post your script - our telepathic powers are too limited to guess how to modify your script without knowing it! But you're lucky: I'm receptive today, so I can visualize something like the code below to modify your script:

var jumpInterval: float = 5;     // interval between jumps (seconds)
private var nextJump: float = 0; // time to jump again
...
    // modify your jump control this way:
    if (Input.GetButtonDown("Jump") && Time.time > nextJump){
        nextJump = Time.time + jumpInterval;
        // here goes your current jump code
    }
...

Hope my extrasensory power is correct, and this can help you. If yes, I'll risk some money in the lottery today; if not, please post your current script.