I explicitly tested this scenario last week. The system has a single eligibility time that it sets when you book a LL reservation. The expiration of a reservation is only indirectly tied to eligibility time, sometimes.
Every time you book a G+ LL reservation, it sets a eligibility return time, which is the earlier of the end of the reservation return window and 2 hours from the current time (or 2 hours from the park opening time if you’re booking before opening time). Every time you book, it sets a new time and there’s only one time it’s tracking.
So if it’s 9:00 am and you book a 10:15-11:15 am reservation, the eligibility time is set to 11:00 am. If you wait until 11:00, the eligibility time hits and you can book, but that new booking sets a new eligibility time. Say you booked a 11:30-12:30 at that point. Now your eligibility time is 12:30. If you wait until 11:15, nothing happens. You can still tap in and regain eligibility, but the expiration of your 10:15-11:15 reservation does nothing, because that was never set as an eligibility time in the first place.
The confusion arises because tapping in on any reservation resets eligibility, and canceling any reservation resets eligibility, so it’s easy to think that expiration of any reservation would reset eligibility. But it doesn’t work that way.