I got mine done by birds at 87k miles ish.
Apparently they weren't too bad, probably due to a lot of motorway miles and comparatively few short trip driving. Meth and oil catch can were fitted too recently to make a difference.
I hear every 50k miles is a reasonably interval for cleaning. I probably won't keep mine that long, on 95k now.
2008 E90 335i LCI M Sport / Manual / Black / Red Leather / Avon ZZ3 / VMR710
Mods: JB4 / BMS DCI /AR Design DPs / ETS FMIC / Water Meth Injection / BMS Chargepipe / BMS OCC / Cool Carbon Brake Pads / Rob Beck PCV Valve / Forge Diverter Valves
Wish List: LSD / Bastuck Quads / Birds Suspension / M3 Arms