Destroy object when it is in space for certain time continously

Hy. i am making a game like endless runner…i am supposed to destroy object when it falls from the ground…but when it leaves the ground msg shows of falling but if it will again touch the ground then the game continuous playing…i want that if it once leaves the ground for certain time then the object destroys… plz help

You could use an OnCollisionExit method to check to see if it is hitting anything, if it is not then you can set a boolean to false and run a timer from this. If the time is less than your desired time, destroy the object.