This all depends how damaged your nails are and what caused the damage in the first place. However, with regular, daily hand and nail care you can get your nails back to top health in a couple of months. This time allows the nails to breathe and fully grow out. Make sure you add nail treatments, like nail hardeners and oils, into your routine as this prevents breakages and helps with regrowth.
Also stay away from the acyclic and glue on false nails as these can cause more damage. Instead, keep them short and file them to avoid ridges and breakages.