Do you think a city should have the power to ignore daylight savings time entirely, or should the state have the power to regulate all its cities? Where do you draw the line?

In practice, I imagine if California passed a state amendment fixing themselves to PST, the federal government would either change the law or refuse to enforce it. Opposing such an amendment would be pretty unpopular.

But in theory, the federal government does have power to "fix the Standard of Weights and Measures" nationwide. I see no reason for a court to rule this as being outside federal jurisdiction.