Not all first cleans are equel, some might have not seen a windie for Ten years, be by the side of a busy road under a cloud of powerstation ash, others may have been done by WFP two months ago, I usually allow up to three times as long on a first clean which with talking to the customer and trying to be as professional as possible could easily be an hour on a £10-£15 job as posted, if you are converting a lot of trad jobs, yes they will take a bit longer than normal but not the three times, also you might have the benifit of some of the houses been similer and a lot of the usual problems are overcome,(such as access,snags,hidden windows,etc),
I cant believe many WFP's rush first cleans as we will have all seen the issues that can arise but if your expecting a high fall out from the trad conversion you might get away with it.