Gurdurr and Conkeldurr learn the same moves at the same levels, so there's no reason to wait to evolve it as its stats will be better. The same goes for Boledore to Gigalith. Plus, they learn some additional tms in their final forms and there are none that you can no longer learn. So, always evolve Gurdurr/Boledore as soon as you can, because it will open up more move options and improve your stats.
