law: 4. References to time of day.-
  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.