Since the LB17 contains lactobacilli (which is what the whey supplies in NT), I would think the fermentation length would be about the same. Generally approx 2-4 days at a 72 degree temp, more for colder and less for warmer. Not sure if because LB17 supplies lactic acid already if that would speed the process? Maybe just have to experiement, but about 3 days should be a good average at room temp and then transfer to cooler storage 40 degrees.
Hope that is of some help. Interesting combination, let us know how it turns out.