how often is the unity ad ready?its a rewarded video ad which gives 1000 cash to the player.

using UnityEngine.Advertisements; public class admanager : MonoBehaviour { private void Start() { if(!Advertisement.isInitialized) { Advertisement.Initialize("3009385"); } } public void showVideoAd() { if (Advertisement.IsReady("rewardedVideo")) { Advertisement.Show("rewardedVideo"); PlayerPrefs.SetInt("Currency", PlayerPrefs.GetInt("Currency", 0)+1000); } } }