Thanks for the input, guys and gals.
I ended up throwing the starter in the fridge after about 26 hours on the stir plate. I pulled it out when I mashed in the next morning, and while it was still cloudy, a nice later of yeast had settled on the bottom - good growth. I decanted a small amount into a glass to taste, the starter "beer" was much more mild than other starters I've done, and barely tasted of anything - so I then decided to pitch the whole shabang @ 66° the very same day.
Fermentation was vigorous and began after about a 6 hour lag. I just checked the gravity last night, spot on at 1.012 (OG 1.050) — so that's around 76% apparent attenuation. It's only been in the carboy for twelve days and provided that it doesn't drop any more by tomorrow night, then I'll rack and bottle it. Pretty sure it's done, though... The sample tasted pretty good too. The American Hefe yeast has less banana and clove than Bavarian strains as advertised.