Testing Cryptographic Algorithms on a PC

I am trying to test some cryptographic algorithms such as AES , RSA , ECC on my windows PC. What I am doing is like this.

watch2.start(); String EncMsg= AES256Test.encrypt(PlainMsg, secretKey) ;  // PlainMsg is 344 byte watch2.stop(); System.out.println("Time Elapsed: : " + watch2.getTime());  // Prints: Time Elapsed: 319 ms.  

As far as I know for the result to be accurate one needs to run the code as many times as possible. Then takes the average time.

For this reason I did the following. I tried to run the code 1000 times

for (int i=0; i<=1000 ; i++) { watch2.start(); String EncMsg= AES256Test.encrypt(PlainMsg, secretKey) ; watch2.stop(); System.out.println("Time Elapsed: : " + watch2.getTime());   // First iteration it prints: Time Elapsed: 319 ms.  // Then for all other iterations it prints Time Elapsed: 0 ms. } 

As you can see for the first iteration I got (319 ms) but for all other iterations I got ( 0 ms ) which is unrealistic.

How can I get accurate performance result ?