C# Creating/Increment Time Variable

I'm trying to create a time based event but am unsure about how to create a time variable. I've done some research and the best I could find is to create a float variable that equals Time.time. I've created said variable assuming it works I'm unsure how to increment the variable. I tried the tried and true timeVariable++ but it didn't seem to work in this case (not that I expected it to). Below is what I currently have:

Code (CSharp):

1.     public float Shield() //Reduces enemy damage to player to 0 for 30 seconds
2.     {
3.         float expirationTimer = Time.time;
4.  
5.         while (PlayerScript.shield == true && expirationTimer <= 30.0)
6.         {
7.             PlayerScript.GetComponent<Renderer>().material.color = new Color(0.0f, 0.0f, 1.0f); //Converts player icon to blue showing active
8.             Laser.damage = 0.0f;
9.             Destroy(gameObject);
10.             return Laser.damage;
11.         }
12.         return Laser.damage;
13.     }

I create the time variable and then jump into the while loop. I'm guessing if I were to add something like expirationTimer = Time.time; it would just keep resetting the variable. I'm not really sure how time works within programming... What I want is for the method to last 30 seconds and have damage revert to its base damage. Secondly, material color do I have to reset that when the method exists or will it exist blue only while the loop is running?

 

did you solve this ???