Not really. A mist coat that dries out too much won't be bonded well to the backer, and delamination, shrinkage cracks, and other problems are possible and likely. If the concrete is not physically dry and crusty, a light coat of Forton before applying backer can help with adhesion. This won't undo shrinkage and other problems from drying, but it can help with minimizing the potential delamination issues.
Is it salvageable if it dries too long?
Not really. A mist coat that dries out too much won't be bonded well to the backer, and delamination, shrinkage cracks, and other problems are possible and likely. If the concrete is not physically dry and crusty, a light coat of Forton before applying backer can help with adhesion. This won't undo shrinkage and other problems from drying, but it can help with minimizing the potential delamination issues.