Music Choppy and Weird

I have a script in C# that plays different peices of music at each hour and when I start it up it sounds really weird. I think its because every frame its checking for time and messing up the audio playing. i have seen other posts covering things along the lines of this problem. I have some code but I'm not sure what to do next. Any help would be appreciated.

using UnityEngine; using System.Collections; using System;

public class TimeMusic : MonoBehaviour {

 public AudioClip song;
 

 // Update is called once per frame
 void Update () {

     int sysHour = System.DateTime.Now.Hour;
     
     if (sysHour == 17) 
         audio.PlayOneShot(song);

 
 }

}