Get real timing in openGL

i want to have real timing in openGL such as when I file a projectiles, it would shoot for 3 seconds before disappeared. I serach the web but unsure how to do it. Which function should I used to get the timing for the projectiles. timeGetTime(); or glutGet(GLUT_ELAPSED_TIME) or others?What is the difference between both of the functions.

Help!!!!!!!!!!!!!!

Does it matter which you choose?
Both seem to return milliseconds of elapsed time since some point in the past.

So, is there any difference between the 2 functions. I want to use the time to count the amount of seconds for projectile to be launch from a gun.

Please tell me you've actually read the manual page for both those functions.