SOED says 'mister' used from middle of 16th as a 'Weakened form of Master originating from reduced stress in use before a name' which suggests it was 'mister' in speech for a long time before it would be written as that. Gives middle of the 18th century as Mr pronounced mister as a title for a man 'without a title of nobility'. A gentleman would be addressed in writing as John Smith Esq. right up till the 1960s.
I'd put money on there being a huge overlap - SOED doesn't say when 'master' dropped out of use as the usual title for a man of a certain rank. I'm sure Restoration Drama men are called Master Horner, and I'm wondering what Defoe, say, or Richardson would use.
Murphy
EmmaD