If the nap is only going to be 30 mins then you should make the 3hrly E. It's fine to either feed early at 2.5hrs as you are doing or (if LO is not properly hungry then) to wait until after the nap. When naps are only 30 mins or so they rarely interrupt E times. Naps of 2hrs can interrupt E times but LOs tend to either eat well before hand or just sleep past the 3hrs and eat when they wake, say at 3hr 15 or 3hr 30.