12z = 7 AM Eastern Standard Time (or 8 AM EDT)
Weather Models use the military designation— 12z or 12 “zulu”.
This is also known as 12 UTC (Coordinated Universal Time) or what used to be called 12 GMT (Greenwich Mean Time).
The 00z and 12z runs are particularly important because they contain new upper air data obtained through simultaneous world-wide launch of weather balloons (radiosondes) that provide direct measurements of the upper atmosphere.
The convention for naming models is the model name|date| time of the model run, e.g., NAM2021081212z