I never got an e-mail at all despite our having an on-site reservation, but roughly 20 days out from my trip, the BOG FP+s for the month I was traveling were "released." (I found this out from a member here, who posted the info. in our trip club thread. She and others, including myself, had been checking the BOG lunch site every day to see if we could make FP+ for our dates. Once she was able to, she alerted the rest of us.) I was able to get on the BOG lunch site and make a FP+ at just the perfect date and time.
(A tip on using the BOG lunch FP+ site, once your dates are "released": it will give you 3 possible time options for the date you choose. Go ahead and reserve one as a placeholder, but if you don't like any of the times you're offered, simply go back, say you want to change the time of your reservation, and keep hitting "refresh" until you're offered a time you like -- the 3 times you're offered will keep changing with every refresh of the page.)