The official deadline is probably the AGM of whichever league the club want / are allowed to join. Given the SL line up announcement date, I guess that will be November some time.
Clearly if it reaches the point it becomes impossible for a new owner to field a competitive side, that could well be it for next season. There's a slight possibility the club may be permitted deferred entry to League One in 2026 - remember that was granted to the Oxford / Gloucestershire merger which never happened,,- but I'm firmly in the land of straw clutching there.