first, you should know that there is no use for an 18/6 veg time (or at least not that I know of). MJ is the type of plant that does photosynthesis (and thus, grows) as long as the light is shining on it. You could have put those 6 hrs of every night towards making your plant bigger. just a heads up for next time
Its all up to you when it comes to flowering. you could have even set it to flowering right from the get-go with no veg time at all. I let my bach of plants growing right now grow for a full 3 weeks, and on the beginning of the 4th wk, switched it to flowering. my plants are a pretty good size now in their 3rd wk of flowering. Let your plants veg according to how big of a yield you are looking for. The longer, the better. What i suggest you do is let 2 of the 4 start flowering now and keep the other 2 in veg for a lot longer. That way, you will have some quick smoke in a couple months and an even larger amount in the following months.
Before you switch to flowering, make sure you have an automatic timer. This is going to be one of your best friends until the plant is ready to harvest. Turning off the lights at different times every day can result in a hermaphrodite (as I'm told) and it will have an effect on the buds.
Don't trim off any of the leaves. How would you like it if you were a pro athlete and I cut off one of your lungs as your mile times dropped? Exactly. PWND.
+rep?