I could change the plugs on my Jaguar AJ-6's in about five minutes - open the hood, pull the plug boots, pull plugs, anti sieze new plugs (longest part of the task), reinstall plugs, reinstall boots, close hood.
Takes me a couple of hours on the V12 though, as I have to release tension on a belt and displace the a/c compressor and remove the throttle pedestal and linkages to the cylinder banks. I can do it without those steps, but it's just easier to get that stuff out of the way. I've lost interest in fighting stuff - if it's in my way, I just remove it.
It's good that your BMW's are easy to work on. I haven't seen a car with a longitudinal engine that was not easy to work on. It's the ones with wrong wheel drive and V6's that are real knuckle busters.