Time Decimalisation
SlabTime was decimalised at the moment it left orbit (see PD), there being no further reason to link personal sleep/wake cycles to what was already an outdated model.
History
Experiments had discovered, as far back as the 1980's that when deprived of any clues as to the day/night cycle, most people eventually settled into an approximate 27 hour rhythm.
Controversy
While there are many well documented, biological reasons for the length of the SlabDay, it has been frequently pointed out that the extra hours were all added during 'peak time' which greatly benefited the media who had been lobbying for longer peak time slots on Earth for decades.
The fact that time decimalisation was sponsored by media conglomerates has never been disputed.