It is a power granted by the “weights and measures” provision of the constitution (or so interpreted). Read the first paragraph the history section of this Wiki

It is a power granted by the “weights and measures” provision of the constitution (or so interpreted). Read the first paragraph the history section of this Wikipedia article for more details: https://en.wikipedia.org/wiki/Uniform_Time_Act https://en.wikipedia.org/wiki/Uniform_Time_Act