The period of time when you’re casually fucking a guy you used to date, and you’re assessing whether or not he has the emotional capacity to potentially be in a relationship with again, and if you even want to try to be anything other than friends who have great sex rock out and celebrate life a couple times a month. Also, it’s so much fucking fun and you don’t want that to stop or change so it’s an excellent way to maximize the fun, to stretch out the observation period. This amount of time is unspecified. Most likely lasts as long as it takes for one of the parties involved to freak out.
Michael, I didn’t say I wanted you to be my boyfriend?! This is still the observation period, I’m observing you, and you are observing me too, really.