When conditions are relatively unchanged, which element will determine the time of a METAR?

None of the above govern the time a METAR is posted which is once per hour at the end of the hour (for automated systems). As this is a condition of relatively unchanged conditions. All things being equal, RVR is the most critical element followed by sky condition and temperature unless icing conditions are present within the airport control area. Altimeter setting is available via VOR(?) Any substantial change triggers a SPECI report, SFAIR.