I guess you would do it like for adjusting for daylight savings. When you make the jump to one nap, it often starts out short (so you need early bed) but as the days go by it lengthens out. That has certainly been my experience, anyway.
Usually I would say 4.5hrs after wake up but I think for a 5am wake up that is too early. So if I were you I would probably do ANYTHING I could do to resettle her at 5am... definitely keep her in her cot until 6am, then turn on the lights/open the curtains and make a big deal about 'morning' and BF. Which makes me wonder - a) is the room totally dark, it's not these early/light mornings waking her? and b) if you rushed in there at 5am and BFed her back to sleep (and back in her cot) at 5am, do you think that would buy you another hour or two? I am mortally afraid of EWs, so if I could get her back to sleep with a 5am feed I would totally do that. Even a 4am dreamfeed.
OK so ideally you would be able to get her back to sleep for at least a little while, and then you would do 4.5hrs A time - nap (as long as possible, try to resettle as soon as you hear her) - then 4.5hrs A time to bed.
If you absolutely can't resettle and the day starts at 5am, I would do a 10.30am nap - again as long as possible try to resettle if you can), then 5.30pm bed. Obviously this route is more likely to continue the OT, so if you can APOP her back to sleep at all in the morning, do so.