How do you know when you abandon ST attempt for the night?

Hi! Starting night 1 of ST our 12 week old to fall asleep independently.

I put my baby down 15 minutes before the wake window ends and she just lays there eyes open, no fussing, just relaxed.

My question is - what do I do if she’s like this for 30-60+ minutes? Not crying. Because we’ve had that happen before in the middle of the night. We’ll put her back in the crib and she’ll be laying there awake for an hour, sometimes 1.5hrs, before she starts crying and then we just rock her back to sleep at that point.

So when starting ST for bedtime, how long do you let them lay there before it’s time to rescue and prevent overtiredness? If they are calm? Same question for if they are crying. Our final wake window is anywhere from 1.5 to 1.75hrs (depends on how well naps have gone).