You know what hun, if you're happy with this routine and it fits in with your family life, I would just go with it for now. As long as the nights are ok and you feel he's well rested?
I personally would wake on the 3hr mark to ensure he got all his feeds in during the day, but with only one nf atm that doesn't seem to be a problem either. Are you bf? Might be worth an extra top up feed 10mims or so before that nap (obviously not feed to sleep), but might be difficult if he's so tired then anyway

All in all, I'd say if it's not broke... But would be interested to hear what others think too. I never got longer than 45mins ever with my DD until she was nearing the 2-1! X