I have grown integrifolia from seed and I am pretty sure that it flowered in 3 years.
I planted it in a herbaceous border where it scrambled about happily enough without making masses of growth. It is some years back and from memory it didn't persist for very long - 3 years max' in the border, as an educated guess.
I am also pretty certain that the flowers were scentless, contrary to received wisdom, but memory isn't infallible.
The seed would have come from one of the UK society seed distributions - SRGC, AGS, HPS.
I am no clematis expert to suggest that integrifolia likes "normal" growing conditions for Clematis in general, but they normally like cool, moist roots and their heads in the sun. (Yes, exceptions - armandii for instance, and montana will grow anywhere.)