What do you do when he wakes at that time? Have you tried to re-paci, pt/sh, or pu/pd? I find re-paci works best for my dd. Have you tried wake to sleep? This could work to get him out of the habit of waking, it may take some time and you would need to do it everyday. I did this for my dd's first nap and after two weeks (she took LONG) it finally worked like a charm.