I use Blackstrap unsulphured molasses too. No problems at all. What I do is, I give it to them every other feeding, because there's some molasses residue left in my watering jugs the second time through, so i figure why add more. After two feedings, there is no more molasses residue and I give them another dose.
It's a fairly subtle effect on the final buds, at least for me. The smoke is slightly sweeter, so if you're not a sensitive taster/smeller, you may not notice much effect.
It won't do any harm to add molasses later in flowering; that's what I did when I first tried it. Of course, that made the effect even more subtle, so that I could barely tell a difference at all. Honestly, the benefit seems so slight that when I run out of molasses, I probably won't buy more. Of course, I did buy a 1-gallon jug, so I probably won't be running out until 2025 or something.