The 5 HP two stage in my garage should be about ready for its first oil change. Ok, it has been since about 1987 as I bought it in 1986.
Honestly,on a shop run compressor that is in a temp regulated building that's not really a big deal as long as the pumped air filtration is adequate.
If the pump oil is dirty black there might be a cause for concern though.
Compressor oil has no viscosity index improvers so shear isn't really an issue and considering the duty cycle,in and off and not consistently pumping means the oil never really gets super hot which can lead to ring coking.
So the oil has been in the pump 30 years and no problems yet here we get guys all worried about 6 month oil change intervals.
I use amsoil because of our duty cycle. The air compressors run steady,not on and off once the tanks achieve pressure,so they are always pumping air since the gas engine is always running. The valve pops once the tanks have been pressurized which then just pumps the air off into the atmosphere.
I've got compressors with more than 10000 hours on them,original Honda 160gx engines and v-twin or triple cylinder pumps and they've never been opened,so my yearly oil changes seem to be doing the trick.
The compressors run in -35 like this morning and 35c in the summertime and the amsoil takes the extremes like a champ.
If your pump isn't exposed to wild ambient temp fluctuations or serious duty then and non detergent sae 30 grade should be fine,and change the oil when it starts turning black.
I put a filter on the crankcase breathers on all my compressors so when it sucks air in its filtered which keeps the oil clean much longer than without.
I make my living with air so my equipment has to work everyday and in this case,due to the extremes,amsoil is king.
Even at -35 the oil pours quite quickly.