Can I add a delay function into an independent function but not in the update?

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What should I do if I want to add a delay function after case AIState.attacking?
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Can I add a delay function into an independent function but not in the update?

E.g. I want to shoot the bullet object (let me call it X) 3 times, which would be like this:
X_X_X (symbol "_" representing a delay, let it be 0.5 second)
Let LoopA = "X_X_X" 
I want to have this loop for 3 times, so it should be like this:
X_X_X - X_X_X - X_X_X, where the symbol " - " representing another delay I need to have.
I've already made this to be a function(let it be function Y) that will be called by switch cases.
Therefore, I need to add delay function into function Y. What should I do?

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Here is the code:

function MakeDecision(){

        switch(state){

            case AIState.wandering:
                Wander();
                break;

            case AIState.chasing:
                Chase();
                break;

            case AIState.attacking:
               // add delay here
                Attack();

Use WaitForSeconds() to delay the bursts of bullets and the firing of each bullet in a burst.

private void MakeDecision()
{
	switch(state)
	{
		case AIState.wandering:
			Wander();
			break;
		case AIState.chasing:
			Chase();
			break;
		case AIState.attacking:
			AttackAfterDelay(3, 0.5);
			break;
		default:
			break;
	}
}

// Delay the first attack (in this case, firing 3 bullets).
// Use same delay between attacks.
private IEnumerator AttackAfterDelay(int numAttacks, int delay)
{
	while (numAttacks > 0)
	{
		yield return new WaitForSeconds(delay);
		FireBullets(3, 0.5)
		numAttacks--;
	}
}

// Fire 1 bullet immediately.  Then delay the firing of all following bullets.
private IEnumerator FireBullets(int numBullets, int delayBetweenBullets)
{
	while (numBullets > 0)
	{
		FireBullet();
		numBullets--;
		yield return new WaitForSeconds(delayBetweenBullets);
	}
}

// Fire a single bullet.
private void FireBullet()
{
	// TODO: Fire a single bullet.
}

This is exactly what I want. Thank you!