Unity Countdown Timer (MM:SS)

Timer.cs

using System;
using System.Collections;
using TMPro;
using UnityEngine;
using UnityEngine.Events;

[RequireComponent(typeof(TextMeshProUGUI))]
public class Timer : MonoBehaviour
{
    private TextMeshProUGUI textUI;
    private float currentTime;
    private bool isRunning = true;
    
    [Header("Events")]
    public UnityEvent timerEnded;
    
    [Header("Control")]
    [SerializeField] private string time;
    
    void Start()
    {
        textUI = GetComponent<TextMeshProUGUI>();

        StartCoroutine(nameof(CountDown));
    }

    IEnumerator CountDown() {
        ConvertStringToTime();
        
        while (isRunning) {
            if (currentTime > 0.5f) {
                currentTime -= 1;
                textUI.SetText(ConvertToTime(currentTime));
            }
            else {
                isRunning = false;
                timerEnded.Invoke();
            }

            yield return new WaitForSeconds(1);
        }
    }
    
    private String ConvertToTime(float seconds) {
        return TimeSpan.FromSeconds(seconds).ToString(@"mm\:ss");
    }

    private void ConvertStringToTime()
    {
        string[] s = time.Split(':');

        float minutes = float.Parse(s[0]);
        float seconds = float.Parse(s[1]);

        currentTime = minutes * 60 + seconds;
    }
}