When to pump while exclusively breastfeeding?

Christina
If im feeding my LO every 2.5-3hrs when should I pump? This is my second child but I'm new to pumping.. any tips? My goal is to pump and freeze so I can start to build up a stash and have plenty on hand when I go back to school (in June). If he's eating so often when is the best time to pump and still have milk for him to breastfeed when he's hungry?