Even though KΤΕL Αttikis filed for bankruptcy in September 2023, buses not on the OASA system continue to run.
Their website has been down for the last few months, but there is no timetable for the Thessaloniki route on older versions of the website either.
KTEL Thessaloniki website also does not have this 23:45 departure on the schedule, but it can be selected when buying a ticket.

A 6 hour overnight trip on this one doesn't seem like a dream...