Thanks for details, that explains why two different FAQs have different values.
Totally know what you mean about it depending on child - at 4 months, mine was ready for 4 hourly feeds but not for 2 hours awake time, but now, at 19 weeks, her A time is exactly 2 hours, she went from managing 1 hr 45 to 2 hrs within a few days, after 3 weeks of managing only 1 hr 45, so it's definitively not a linear process and average A times are only useful to have a kind of idea of what A time could be, cues are of course the thing to follow (but easier to do when you have a time range in mind).