Round Timer: Time.smoothDeltaTime stops the clock...

 using UnityEngine;
 using System.Collections;
 
 public class EnemySpawn : MonoBehaviour {
 
     public float timeLeft = 300f;
     public float roundPause = 60f;
     int numEnemies = 100;
 
     public GameObject enemies;
     GameObject spawnEnemy;
 
     Vector3 pos;
 
     // Use this for initialization
     void Start () {
 
     }
 
     void newRound() {
         for(int i = 0; i < numEnemies; i++) {
             pos = new Vector3(Random.Range (-200, 200), 20, Random.Range (-200, 200));
             spawnEnemy = Instantiate(enemies, pos, Quaternion.identity)as GameObject;
                 }
     }
 
     void OnGUI() {
         GUILayout.TextArea ("" + roundPause);
     }
 
     // Update is called once per frame
     void Update () {
         if (timeLeft >= 0) {
             timeLeft -= Time.smoothDeltaTime;
                 }
         if (timeLeft <= 0) {
             timeLeft = 0f;
             roundPause = 60f;
                 }
 
         if (roundPause >= 0) {
             roundPause -= Time.smoothDeltaTime;
                 }
 
         if (roundPause <= 0) {
             newRound();
             roundPause = 0f;
             timeLeft = 300f;
                 }
 
     }
 }

How it works:

You have a 5 minute round, when the round begins, 100 enemies spawn in. after the 5 Minutes are up, you have a 1 minute intermission (Will probably drop to 30 seconds.) But when I'm lowering the time for the float roundPause, it stops at 59.9843 seconds.