I'm guessing it is an A time issue. You said you got 45 min naps when you extended the first A time til 9, right? I'd push it longer then. Between 5 and 6 mos, most lo's can handle 2.25 - 2.5 hrs of A time. The tired cues that you are seeing at 8:40 could actually be "bored" cues - I noticed around 5 mos that my lo's tired cues were almost never tired cues, and started paying more attention to time cues. Try switching up his activity when he starts to act tired - but keep it really low key. See if you can wait til 9:15 to put him down. I wouldn't extend all that in one day. Just push it 10 min at a time, every other day or so and see how that goes.
If he wakes early from the nap, keep doing what you're doing to try to extend him - looks like you've got a good routine there, and I'd keep doing the only trying for 20 min deal, and then just get him up. If he has a short nap, cut his next A time really short though, or the OT cycle will just build throughout the day. Maybe after the next feed, only keep him up for 30 min, then back to nap. That may mean a lot of short naps throughout the day while you're extending A time, but it will fight off the OT disaster.
Other than maybe too short A time in the beginning, your routine looks really good, so try extending that and let's see what happens. Hang in there!