If you're doing a lot of short runs it's a very good idea to change oil between CBS. I would change oil every 12 months or 12k km. BMW Australia is trying to convince Munich to change the CBS for Australian cars because of the harshness of the weather here.
If you plan to keep the car for long then do it.
2007 E92 6MT - Silverstone II with Extended Black and /// Performance Exhaust and BPM Sport Tune
2011 F25 X3 3.0d