"My" explanation  is the industry standard:  8am setback time is used to assure the marketable title is passed in order to specifically check and verify lien priority WHILE preventing new, unindexed (yet) liens from taking superior position.

 Envision this:  a title company misses the 8am recording deadline and is, for one morning, forced to record 60 documents at the public counter (by check) at 8:15 am, in line with others.  Before those 60 documents can be individually reviewed by the Registrar's staff, the title agent must check the Grantor Grantee Indices of Official Records to ensure that no other liens have recorded in the past few days which is the gap period between title company records and the current county records.  

 In this scenario, 7 members of the public record documents.  Most likely they don't affect the subject 60 documents (which are probably about 25 property transactions).  However, in my scenario, one does and it acquires a 8:04 a.m. time stamp on a $2,000,000 lien.  Furthermore, to add insult to injury, a mechanics lien that has been sitting and awaiting processing in the county's backroom mail bin is picked up by "Larry" and recorded at 8:09 a.m. after he's had his morning coffee and settles down to his routine.  Finally, to really highlight the problem, another title company is recordng another mortgage paper the same morning at 8am.  That 8am mortgage is SAFE as it has a priority of time.  Your late title agent's package is subject wholly to a mortgage, a lien and a mechanics lien.  

This is why it's a race to the counter state:  It makes no sense that two contractors at 4:00 p.m. being served on different counters and getting identical time stamps and one other lien upstairs in the mail processed with the same time stamp are all equal in exact form.  This ruling fails to account for serial  numbers issued in  sequence.  Otherwise, what exactly is the point of issuing numbers in seuqence instead of randomly?

 Also, institutional wrongdoing does not create a lawful custom or tradition:  years of robosigning, forcing minorities to sit on the back of a bus,, or slavery does not legitimize illegal acts, any more than a  service providers' unwillingness to share names between title companies exempts them from liability for claims losses when one goes before another, otherwise I would not have spent 25 years being told by title officers to PULL files from the submission que at 8am, because we found other companies with open orders that needed to be recorded in proper sequence.