You dont have to flower longer, that wouldnt be good for your bud man. I hope you have a scope now to see your trichos. If not you really should get one man, im cheap but I still bought one, only way to know the perfect time to harvest. You can get them at radioshack for about 10$. Hopefully you konw what they should look like when you should harvest. if not check the faqs, or go to youtube, and type in How to judge cannabis, look at jorges, the white guy with dreads, that video helps alot.
But anyways, the best kind of molasses to use is Unsulphered Molasses. And you can use it right until you harvest, becuase its not a chemical, just give the weed a sweet taste : ). Dont use it every watering tho, gotta give your plants time to use it. Every other watering will be fine, maybe every 3rd. But you will see results within a couple days. But deff get a 10x or more scope, and dont flower longer.
You should get alot more crystals though, like an amazingly amount more. PLus your bud will swell up nice and big : )
Get it asap though, and post some new pictures of the improvement, take a before and after picture of the bud to show the world!!
as always good luck buddy