how can i take time value from timer (Asked again clearly)

I have timer and checkpoints in my game i want to write down moments when player passes this check points i can handle with text things it is easy but i cant write down time when timer still working is it possible i want to give example now time starts and you reach first checkpoint at 00:11:12 and second 00:22:44 third 00:35:32 it will be shown like this

1. Current Time : 00:35:32 (same with third checpoint 1.Check : 00:11:12 2.Check : 00:22:44 3.Check : 00:35:32

There is part of my timer Script corresponding i search everywhere but couldn't find thanks a lot

      if(SceneTestMap.GetComponent<SceneTest_Map>().checkPoint==1)
      {
     
         checkPoint.text = TimeToString(?????);
      }

this is the whole script

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
  public class Timer : MonoBehaviour {
  
  public Text timerText;
  private float startTime;
  public GameObject SceneTestMap;
  public Text Hedef_74text;
  
      bool keepTiming;
      float timer;
  
      void Start () {
          StartTimer();
      }
  
      void Update () {
          if(SceneTestMap.GetComponent<SceneTest_Map>().IsRaceFinished == true){
              Debug.Log("Timer stopped at " + TimeToString(StopTimer()));
          }
  
          if(keepTiming){
              UpdateTime();
          }
          if(SceneTestMap.GetComponent<SceneTest_Map>().checkPoint==1)
          {
         
             checkPoint.text = TimeToString(?????);
          }
      }
  
      void UpdateTime(){
          timer = Time.time - startTime;
          timerText.text = TimeToString(timer);
      }
  
      float StopTimer(){
          keepTiming = false;
          return timer;
      }
  
      void ResumeTimer(){
          keepTiming = true;
          startTime = Time.time-timer;
      }
  
      void StartTimer(){
          keepTiming = true;
          startTime = Time.time;
      }
  
      string TimeToString(float t){
          string minutes = ((int) t / 60).ToString();
          string seconds = (t % 60 ).ToString("f2");
          return minutes + ":" + seconds;
      }
  }