People have an obsession with this time, call it the witching hour etc. I think it is because it is the point between night and day, or rather the previous day and the next.
These 'between/in the foot of two things' seems to be an obsession with a few practitioners, I have no idea if this is a modern invention or has historical basis.
It may also be that in most areas, midnight is a quiet time and you can gt on with your work in peace! I know a few modern athors who will practice at 3AM these days because people don't go to bed at 9PM like they did back in the day- less folk shouting etc. and disrupting your work.
In my system the hours of the day and night are assigned to a planetary energy, this changes every day, and so midnight isn't just significant for one reason, but for many depending on the day.
^That is a great article on what I am talking about.