Maryn
I don't really believe in A times per se. I believe in watching your child very closely for the very subtle sleepy cues and I really believe in set naps because there is research that says that children are ready to nap at certain points in the day and that gives the most restorative naps.
However 10 months is notorious for having sleep regressions, but I still believe in sticking with a consistent routine, but being flexible and NOT pushing a baby if they are tired and need sleep. I really, really believe in super early bedtimes too.
But, naps are stubborn creatures and once they are 'broken' for lack of a better word, they take awhile to fix as oppose to night sleep which can be fixed relatively quickly.
From everythign you are saying, your DD is not just tired, but OT. 3 hours is still too long for her to be going, especially when OT.
This is what I would do...and it's just my 2 cents so take it or leave it.
If she wakes earlier than 6am and you can't get her back to sleep then aim for a nap around 8:15-8:30. If she wakes later in the morning, then nap at 9am
2nd nap-depends on time and quality of first nap but if the first nap sucked and was under an hour then I would start nap #2 around 12:15-12:30. If the morning nap was decent and she's looking good, then I would try to stretch it to around 12:45 but no later than 1pm.
Then depending on the quality and length of both naps,I would do bedtime no later than 3.5 hours from wake up of the pm nap. I would actually err on the side of caution and do bedtime even earlier actually. But really watch her for cues and get her to bed pronto if you see anything-eye rubs, yawns, staring into space, zoning out or worse-signs of OT-hyper, silly, buzzed or super cranky.
Hope that helps.