We just today got an 8am BOG reservation for April 16th. So seems they are still available for at least April...Beginning in April or May no one has been able to book BOG before 9 am so that is the change. There are other threads about it in the restaurant chain I think. No one knows if it’s temporary or permanent or a glitch.
ETA Here is one of the threads. Can’t find the other.
https://www.disboards.com/threads/bog-only-showing-1-time-available-for-our-whole-week-9-am.3654026/