In this Act, references to time of day are references to Indian standard time, being five and a half hours ahead of Greenwich mean time:
     Provided that, for any area in which Indian standard time is not ordinarily observed, the Central Government may make rules--
         (a) specifying the area;
         (b) defining the local mean time ordinarily observed therein; and
         (c) permitting such time to be observed in all or any of the mines situated in the area.