My DD is a similar age but 1 week OD, and her A times have always been on the low side, just like her big brother's, so actually they're still only 2h 40, but that works for her. Bear in mind that the average/typical A times are just that, some will do more, others less. So tbh I don't think it's so much a case of whether to do a 6mo or a 7.5mo routine, by all means use these as a guide, but it's what she can manage. My DD will also chat quite happily to herself in her cot if she wakes early or after a nap, provided she's not in discomfort. Due to having to fit around preschool drop off, we have a fixed 'WU' time (so if she wakes early we just let her chat to herself, since she's happy) and a fixed time for her first nap, which also worked quite well for DS who was similar. So she does get more A time if she wakes early but since she's calm and relaxed it doesn't seem to matter. But she is being carried in the sling on the way to and back from preschool for the end of that A time, and we even take her out at that time at the weekend as it's her routine and helps her to stay calm until her nap time even if she would otherwise get worked up from OT - we actually did the same with DS. Just another idea to consider, we also used the 'half A time' concept with DS which worked quite well. In your scenario above I'd have probably gone for the nap to start sleeping around 9.30 but carried her around to keep her calm, since her 45min nap sounds UT to me. But having had that, if you got her up after the 45 mins playing I'd have gone for the next nap between 1.5-1.75h after that depending on cues, to take into account the 'half A time' but also the fact that her effective A time would need to be a bit shorter after the short nap to avoid a UT/OT cycle.
With regards to the crying at 20min intervals, that can be a sign of discomfort, do you think that could be the case here? But it can be OT/UT... You know her best!
