Countdown Timer checks not working

Hello, so I was making a tutorial popup script today, it all works perfectly fine until it comes to checking if my timer has hit 0 or not. It should be working but for some reason, it doesn't want to. What the code is designed to do is cycle through the popups but in 3 & 4 (popUpIndex 2 & 3) they use a timer but it doesn't toggle the next one as the timer hits 0.
If anyone could help that would be greatly appreciated.

 void TutorialLevel1()
     {
         for (int i = 0; i < popUps.Length; i++)
         {
             if (i == popUpIndex)
             {
                 popUps[i].SetActive(true);
             }
             else
             {
                 popUps[i].SetActive(false);
             }
         }
 
         if (popUpIndex == 0)
         {
             if (Input.GetKeyDown(KeyCode.W))
             {
                 popUpIndex++;
             }
         }
         else if (popUpIndex == 1)
         {
             if (Input.GetKeyDown(KeyCode.A) || Input.GetKeyDown(KeyCode.D))
             {
                 popUpIndex++;
             }
         }
         if (popUpIndex == 2)
         {
             popUpTimer = 5f;
             
             if (popUpTimer <= 0)
             {
                 popUpIndex++;
             }
             else
             {
                 popUpTimer -= Time.time;
             }
         }
         else if (popUpIndex == 3)
         {
             popUpTimer = 5f;
             
             if (popUpTimer <= 0)
             {
                 popUpIndex++;
             }
             else
             {
                 popUpTimer -= Time.time;
             }
         }
         else if (popUpIndex == 4)
         {
             //Hide When mission complete!
         }
     }