I used it from week 2 of flower through week 7. The last week nothing but h20.
can't compare the results though as I also started using hydro nutes on my last soil grow. I ended up with around 50% more weight from slightly smaller plants than my first. That comparison is no good as well, as I also topped and FIMed and ended up with many more big buds. Hell, the differences between my first and second grow were night and day. I made so many mistakes on my first I'm surprised they did as well as they did.
Here's something important to keep in mind in case you didn't already know. Mix your molasses with a cup or two of very hot water to dissolve it better. Then mix with the rest of the water that you plan on using. I use 2 tablespoons per gallon of water, but I suspect you could probably use more. Also, don't let your molasses and water sit out for 24 hours unless you plan on feeding your plants an unhealthy dose of bacteria.