Wouldn't the most correct translation technically be"You may..." instead of "you can" since it is obvious that the possibility of doing the action exists, unless the person is in prison.
Like "You can eat now" is actually not as correct " you may eat now." Just my two cents.
It doesn't seem to be as much an issue of which is correct, as which is more formal or informal. These links explain it:
If you Google "can versus may" you'll find even more. :)
Assuming this isn't just a Duolingoism, any of our more fluent peers know what connotation this would have? It sounds like halfway between granting someone permission to be excused and dismissing someone. Or is this just one of those sentences no one would use in the normal course of the day?