Leaving it for a couple of weeks before bottling accomplishes 2 things:
1) allows the sugar to thoroughly mix into the wine, and
2) allows you to make sure your stabilizing (kmeta and sorbate) worked and to prevent any of the yeastie beasties from fermenting the sugar you just added. If that were to occur in the bottle, you could get bottle bombs, and leaking or exploding bottles are not a good thing.
If you have the carboy topped up and under airlock, the chances of wild yeast causing fermentation to restart is slim.
But it's your wine and your risk tolerance. If bottling right after backsweetening is working for you, then go for it.
I have sometimes bottled right after sweetening but my current protocol is to rack to a bucket, add kmeta and sorbate, add the sugar or simple syrup, then rack back to a carboy and let everything meld together for a few more weeks before bottling.