I obviously don't know exactly how the calculations are done, as I don't have the algorithms, but it seems to me from examining the sleep data available to me on the website for me personally that this is how it works regarding wake time:
Example: If I wake in the morning, and then am awake for some period of time (say 20 minutes) before I decide that yes, it's time to rise and that no, I won't sleep any longer, then that 20 minutes is counted as "time awake" in the tally of the various sleep stages for that night's sleep.
In reality, of course, I wasn't awake for 20 minutes *during* my sleep time, which would obviously represent some decrease in sleep quality. I had simply awoken and lay in bed for 20 minutes, perhaps just seeing if I might doze off again, before rising definitively. This 20 minutes clearly shouldn't be counted as "wake time" during the sleep period, as waking up early will already affect the calculation for ZQ etc. merely be having a shorter sleep period.
Can anyone clarify what actually happens with the calculation? It seems to me that it should be the case that any "awake" periods that happen to end the sleep period data for a night ought to be discarded from any "awake time" calculations, as that bit of awake time is, of course, irrelevant to sleep quality in and of itself. Leaving that data in would obviously skew the calculations, including ZQ, but more importantly, the amount of time presented as being "awake" during the sleep period.
Likewise, wake time during the "time to Z" period ought not be included, either, but should be presented separately from the data for the sleep period proper. Even if I take 3 hours to fall asleep, if I then sleep well for 9 hours, the time to Z shouldn't affect the quality of the sleep as a matter of fact.
I'd try this myself, but then I'd have to sacrifice a night's (or two or three) worth of sleep data in order to find out!