Trying to get a beer to be done/ready to bottle on a human imposed time frame is not wise. Chances are it won't work out that way either. As for how long a batch will take, that depends entirely on the recipe, how it's made, conditions where it's fermenting, and more. While I have had a batch finish fermenting in less than a week, I won't move it to keg (or bottle if I was still bottling) at that point. I give it some more time to allow other great things to happen. Such as the yeast do a bit of house keeping in the form of cleaning up any off flavors it might have produced (there are yeast strains that require this rest period). Another is to flocculate out of the beer so that you transfer more beer into keg/bottles. If it takes another week, or several, for this to happen, for a batch I've brewed, then it's going to get that time.
My 'normal' range of time in primary has been 2-12 weeks. I have a big barley wine planned for the end of this month that could go even longer.
BTW, just adding more sugar can be harmful to the recipe in more than a few ways. Depending on the percentage of the recipe is going to be plain sugar, it could turn the brew cidery. It can (or will) thin out the body of the brew and throw hop utilization off. IMO, better to enter the recipe into software to see what your conceived changes will do to it. IF you want to make a stronger brew, you're better off adding some DME to the recipe, instead of sugar.