Message Centre Does Not Display

@BackslashOllie I had updated the code but now the message centre main time of day greeting does not display?

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 public class MessageCentreManager : MonoBehaviour {
 
     int sysHour = System.DateTime.Now.Hour; //gives you the current hour as an integer.
 
     //UI Text Reference
     public Text MessageCentreText;
     
     //Button States
     public int buttonState = 0;
     bool GreetUser = true;
 
     void Awake ()
     {
 
     }
     
     void Update () 
     {     
         if (GreetUser) ShowGreeting();
         if (buttonState == 1) MessageCentreText.text = "SCANNING";
         else if (buttonState == 2) MessageCentreText.text = "AUTO PHONE";
         else if (buttonState == 3)  MessageCentreText.text = "INT TEMP";
         else if (buttonState == 4) MessageCentreText.text = "LASER FIRE";
         else if (buttonState == 5) MessageCentreText.text = "TURBO MODE";
         else if (buttonState == 6) MessageCentreText.text = "OIL SLICK";
         else if (buttonState == 7) MessageCentreText.text = "AUTO SCAN";
         else if (buttonState == 8) MessageCentreText.text = "TRIP TIME";
         else if (buttonState == 9) MessageCentreText.text = "RADAR";
         else if (buttonState == 10) MessageCentreText.text = "CNTDWN TIMER";
         else if (buttonState == 11) MessageCentreText.text = "EXT MOVIE PLAYER";
         else if (buttonState == 12) MessageCentreText.text = "GRAPL HOOK LAUNCH";
         else if (buttonState == 13) MessageCentreText.text = "AUTO DOOR LFT";
         else if (buttonState == 14) MessageCentreText.text = "AUTO DOOR RHT";
         else if (buttonState == 15) MessageCentreText.text = "PENG";
         else if (buttonState == 16) MessageCentreText.text = "7DLA";
         else if (buttonState == 17) MessageCentreText.text = "6RM";
     }
 
     IEnumerator ShowGreeting()
     //void ShowGreeting ()
     {
         //Time OF Day Notification
         //Morning Time
         if (sysHour >= 01 && sysHour <= 12) {
             MessageCentreText.text = "GOOD MORNING";
             Debug.Log ("Good Morning!");
         }
         //Noon Time
         if (sysHour >= 12 && sysHour <= 18) {
             MessageCentreText.text = "GOOD AFTERNOON";
             Debug.Log ("Good Afternoon!");
         } 
         //Night Time
         if (sysHour >= 18 && sysHour <= 24) {
             MessageCentreText.text = "GOOD EVENING";
             Debug.Log ("Good Evening!");
         }
         
         else{
             //Do something if desired
             MessageCentreText.text = "KNIGHT INDUSTRIES 2000";
             Debug.Log("KNIGHT INDUSTRIES 2000");
         }
         yield return new WaitForSeconds(5); //Wait 5 seconds
         GreetUser = false;
     }
     
     
     //Scanner Button For Message
     public void GoScannerMessage()
     {
         buttonState = 1;
     }
 
     //Car Phone Button For Message
     public void GoAutoPhoneMessage()
     {
         buttonState = 2;
     }
 
     //Temperature Button For Message
     public void GoTemperatureMessage()
     {
         buttonState = 3;
     }
 
     //Laser Button For Message
     public void GoLaserMessage()
     {
         buttonState = 4;
     }
 
     //Turbo Boost Button For Message
     public void GoTurboBoostMessage()
     {
         buttonState = 5;
     }
 
     //Oil Slick Button For Message
     public void GoOilSlickMessage()
     {
         buttonState = 6;
     }
 
     //Surveillance Mode Button For Message
     public void GoSurveillanceModeMessage()
     {
         buttonState = 7;
     }
 
     //Trip Timere Button For Message
     public void GoTripTimerMessage()
     {
         buttonState = 8;
     }
 
     //Radar Button For Message
     public void GoRadarMessage()
     {
         buttonState = 9;
     }
 
     //Countdown Timer Button For Message
     public void GoCountdownTimerMessage()
     {
         buttonState = 10;
     }
 
     //Movie Player Button For Message
     public void GoMoviePlayerMessage()
     {
         buttonState = 11;
     }
 
     //Grappling Hook Button For Message
     public void GoGrapplingHookMessage()
     {
         buttonState = 12;
     }
 
     //Auto Door Left Button For Message
     public void GoAutoDoorLeftMessage()
     {
         buttonState = 13;
     }
 
     //Auto Door Right Button For Message
     public void GoAutoDoorRightMessage()
     {
         buttonState = 14;
     }
 
     //PENG Button For Message
     public void GoPENGButtonMessage()
     {
         buttonState = 15;
     }
 
     //7DLA Button For Message
     public void Go7DLAButtonMessage()
     {
         buttonState = 16;
     }
 
     //6RM Button For Message
     public void Go6RMButtonMessage()
     {
         buttonState = 17;
     }
 
 }