I would ignore the instructions to rack to the second vessel. Leave it in primary for 3 weeks, then pull a sample, test with the hydrometer and taste it (the sample).
What are you making? Depending on what the brew is, what yeast you're using, and the temperature the wort/beer is fermenting at you could need more, or less, time than the instructions say. This is why I hate them so much. If you have super-tight fermentation temperature control, your brew/batch could be ready for bottle/kegs in far less time. But that still depends on what you're making.
There's tons of postings about people racking, or not racking, as per the instructions. IMO, those instructions (for beer) are outdated methods UNLESS you need to move the brew onto, or off of, a flavor element that works best when off the yeast cake. Or when you plan to use extended aging on a batch (more than a couple of months).
For reference, I've had batches sitting on the yeast for almost 8 weeks (range is usually 4-7 weeks) so far. Never once has a batch had any issue or been anything less than great. I have racked a couple/few batches onto oak chips/cubes (prefer cubes) and also had great results. Of course, you need to be careful when racking so that you don't oxidize the beer, or pick up something nasty (that you don't want). While it's still in primary, you have the benefits of the layer of CO2 over the beer keeping things out.
Things I don't rack to add to a batch includes dry/whole hops as well as flavor elements that can stay in there (such as maple syrup).
I would also advise, when it's time, weighing your priming sugar, and using one of the online calculation tools to figure out how much you should add. This site
is just one of the better tools to help you figure out how much to prime with.