As per the provisions of Accounting standard 1, the company is required to follow uniform accounting policies. Therefore the company is required to apply consistent accounting policy from period to period. A change in method of depreciation can be made only if it is required by law, or for compliance of accounting standard, or if change is necessary for better presentation of financial statements.
As per accounting standard 6, when there is change in method of depreciation, depreciation should be recalculated as per new method from the date when asset is put to use.
There you are required to calculate the depreciation from the date when asset is put to use. And the deficiency or surplus arising from recomputation of depreciation should be charged to Profit and loss account in the year of change i.e. in 2017.