Simple Day Night Cycle Efficiency Check

Hi there, I'm looking to make a game in which the time of day can determine an npc's behavior. I wrote a little script that will keep track of time, but it may be relying on the Update method a bit too much. Is there a better place I can put my code for best practice?

 public class TimeKeeper : MonoBehaviour
 {
     public float currentTime;
     public string partOfDay;
 
     private void Start()
     {
         partOfDay = "morning";
     }
     void Update()
     {
         currentTime = Time.time;
         if (currentTime > 50 && (partOfDay == "morning"))
         {
             partOfDay = "noon";
             SetRoutine();
         }
         if (currentTime > 100 && (partOfDay == "noon"))
         {
             partOfDay = "night";
             SetRoutine();
         }
         if (currentTime > 150 && (partOfDay == "night"))
         {
             partOfDay = "morning";
             SetRoutine();
             //currentTime = 0;
         }
 
     }
 
     void SetRoutine()
     {
         //This is where I will update the NPC's to move to a new location
         Debug.Log ("the time has changed to " + partOfDay);
     }