I'm as interested as you in the other replies you'll get to this
question. For my own part, I have been fermenting reds in open vats
(typically 50 gals of must). I have been adding ML (pitched straight
in, not started) late in in the primary - typically just a few days
before I press and take to secondary. The MLF appears to continue for
quite a while in secondary, although varies with each batch of wine.