Well, a coated tongue certainly is a very commonly stated symptom of fasting detox. The return of a coated tongue to normal pinkish color along with the return of hunger are usually the signs one looks for as signals that the body is ready to break the fast.
However, as I've stated before, the feeling of the return of true hunger most often doesn't occur for the average 1 to 3 week faster. The return of true hunger is not just a sign that the body has detoxed as much as it can during a fasting session but a sign that the body has used up whatever reserve it has to sustain your body and will now procede into the state of true starvation unless the fast is broken within the next day. The average faster will seldom reach this state.
If you can, wait until your tongue regains its healthy color (assuming the true hunger sensation doesn't occur first), then I would say it was up to your own sense of judgement as to when you want to break the fast, only of course, up until the point that you may in fact get that true hunger sensation, upon which it is time to absolutely break the fast.
Again, it's wise to have any fast longer than 7 to 10 days supervised by a professional, especially if one intends to go the distance, but of course you know this. :-))