How do I get all of my code in start function

I need to put all of my code in the start function but I am getting an error : CS1525 symbol private . When I put the code in the start function the error came up at the bottom. Here is my code :

public class MyClock : MonoBehaviour
 {
     public int  Minutes = 0;
     public int  Seconds = 0;
 
     private Text    m_text;
     private float   m_leftTime;
 
     private void Start()
     {
         m_text = GetComponent<Text>();
         m_leftTime = GetInitialTime();
     if (m_leftTime > 0f)
         {
             //  Update countdown clock
             m_leftTime -= Time.deltaTime;
             Minutes = GetLeftMinutes();
             Seconds = GetLeftSeconds();
 
             //  Show current clock
             if (m_leftTime > 0f)
             {
                 m_text.text = "Time : " + Minutes + ":" + Seconds.ToString("00");
             }
             else
             {
                 //  The countdown clock has finished
                 m_text.text = "Time : 0:00";
             }
         }
     
 
     private float GetInitialTime()
     {
         return Minutes * 60f + Seconds;
     }
 
     private int GetLeftMinutes()
     {
         return Mathf.FloorToInt(m_leftTime / 60f);
     }
 
     private int GetLeftSeconds()
     {
         return Mathf.FloorToInt(m_leftTime % 60f);
     }
 }

Why is it important that all of the code needs to be in Start()? The code is dealing with time on a per frame basis, this would be ideal in the Update function.