he only reference that I see with regards midnight is this

Quote

Note that the date September 6, 3114 B.C. began at midnight of the previous day, J.D. 584283.5; at noon on that date, it was J.D. 584284, and at midnight, J.D. 584284.5

Which appears to be referring to our calendar system, in which we denote a day being from midnight to midnight. As you can see the Julian date system (which astronomers use) each day starts at an integer value, with midnight corresponding to 0.5 value. perhaps though I missed where it stated that the Mayans started their day at midnight.

To me, it would make more sense for a "primitive" culture (lacking accurate time keeping devices) to map out a day as being the time from sunrise to sunrise, or sunset to sunset, or from when meridian to meridian. The latter would give a more consistent length of day though (inconsistency arising from the equation of time). That doesnt mean that this should be the case though.

Jonny

The path to good scholarship is paved with imagined patterns. - David M Raup