Start to Update() after X seconds

Try shifting all the logic you would usually put in Update into a coroutine that gets set off by Start. That way, you can put a

 yield WaitForSeconds(x seconds);

before beginning on the rest of the logic! There is no way to actaully delay the Update function without freezing the entire game- but there are plenty of ways to achieve what you are trying to do without doing that.

I prefer coroutines for tasks like these.

• Start() Your starting point that will run 3 waves of monsters. After for loop, show a victory screen for example.

• BeginWave(var wave : int) Put setup code for the wave there, like spawning enemies or changing the music.

• RunWave(var wave : int) Put update code the wave inside the while loop. Remember to yield; or it crash.

• EndWave(var wave : int) Put cleanup code for the wave there, like removing enemies or changing the music.

The WaitForSeconds are optional and was only meant to illustrate how you can delay the code at various points.

 function Start() {
     for (var wave = 0; wave < 3; ++wave) {
         yield BeginWave(wave);
         yield RunWave(wave);
         yield EndWave(wave);
     }
 }
 function BeginWave(var wave : int) {
     // Set up the wave, if needed...
     yield WaitForSeconds(5);        
 }
 function RunWave(var wave : int) {
     while (true) {
         // Update your game logic as before.
         // 'break;' (or 'yield break;' if in nested loop) to end wave.
         yield;
     }
 }
 function EndWave(var wave : int) {
     // Clean up the wave, if needed...
     yield WaitForSeconds(5);
 }

Or if you are more of a compact code fan (I'm not):

 function Start() {
     for (var wave = 0; wave < 3; ++wave) {
         // Set up the wave, if needed...
         yield WaitForSeconds(5);
         while (true) {
             // Update your game logic as before.
             // 'break;' to end wave.
             yield;
         }
         // Clean up the wave, if needed...
         yield WaitForSeconds(5);
     }
 }