i think 8 weeks might be come the norm, once custy realise that there windows are clean after 4 weeks, i am thinking of putting every one on 6 week cycle, sort of in the middle, i dont think the winter help where some custy waited 2-3 montsh to get there windows cleaned and realised that they stay clean,
i woudl rather put a custy on a 8 week cycle than lose them all together