Delay alert when waiting for Advertisement.isReady()

Hi, this is my first question - so sorry if I am duplicating anything here.

I am working to show a page where the user opts in to view an ad. I am using the code below to either play the ad when the next page loads or - if there is no internet connection - show an alert page with a friendly message when the page loads. I also initialize Unity Ads on my Menu page.

This code (below) is working - but I'm concerned that the alert might kick in before .isReady() is true if connection is slow. Please could you tell me if I need to delay the alert, and if so, what's the best code to use. Thanks

<code>

using UnityEngine;
using System.Collections;
using UnityEngine.Advertisements; // Declare the Unity Ads namespace.
using UnityEngine.SceneManagement;


public class RCGShowAd : MonoBehaviour
{
// Define gameId as a public field
// so it can be set from the Inspector.
public string gameId;

void Start ()
{

if (Advertisement.isSupported) { // If the platform is supported,
Advertisement.Initialize(gameId); // initialize Unity Ads.
TryAd();
}
}

public void TryAd()
{

if(Advertisement.IsReady())
{

Advertisement.Show();
}


else
{
SceneManager.LoadScene("CS_Alert");
}

}

}