With my 3 they would have been okay to wait until after the nap (assuming that you have reached a 3 hour easy) - our feed times were basically fixed unless there was some big reason not to be. So feeds were at 7, 10, 1, 4, 6.30 (because there was no keeping them awake any longer!), and sleeps were roughly 8.30, 11.30, 3.30. I must confess mine never did so well with shortening a times after short naps, so maybe if that had worked for them then I would have had more trouble getting the feeds fixed.