Garage queen, how often to change the oil

The cars in question are BMW 550i 2009 and 2010. Both have V8 4.8 naturally aspirated engine. There is no oil temp monitoring , but one could make fun needle (gas mileage) to show engine temperature as in 650i. I believe this is coolant temp and not oil temp (something to read on). Coolant temp could also be monitored via hidden menu in the instrument cluster. Perhaps using the phone app I could monitor both easily (need to look into this).
I keep the same schedule as always for my TL (5000 miles). I don't know if it is full 'garage queen' status, but I only drive it about once a month currently.