How to activate/deactivate object in if statements?

I am trying to make an object start invisible/ deactivated, and then after 4 seconds set it as active. I have the below code, but am very lost on how to make this work. Any help is much appreciated!!

void Start(){
	gameObject.SetActive (false);

void Update(){
	if (Time.deltaTime > 4s)
	{ = true;
	else if (Time.deltaTime < 4s)
	{ = false;

change = false to gameObject.SetActive(false)

your time should also be in descending order .