Depends what you mean by "evolve" - in one sense you have "evolved" compared to your parents. But in general it depends on the pool of variation and the selection pressure, so for instance you can expect flocculation characteristics to "evolve" pretty quickly as there seems to be quite a variation in flocculation among the typical yeast population, and it's easy for humans to exert extreme selection pressure on it. So when British breweries switched from top-cropping open fermenters to conicals where they bottom-cropped, they found that their yeast pretty much switched from top-fermenting to bottom-fermenting overnight.
Flavour is more complicated, as it tends to involve gene pathways so there tends to be less variation at the phenotype level to work on, and unless you're picking out single CFUs to trial then you don't get the same selection pressure (unless it's something really obvious like phenol production). And some strains are more subject to variation than others - Pinot Noir is notorious for it in the grape world. But anecdotally, in commercial breweries that are repitching yeast every week they get something that's regarded as a different strain within 10-20 years or so.
There's a lot of working going on at the moment in this field, as the ability to sequence genomes cheaply has transformed our ability to trace these kinds of genetic changes over generations. It's early days yet so not much has been published,
@suregork will be more aware than me of what's bubbling under the surface.