The Constitution give Congress (Article I, Section 8, Clause 5), the power to set Standards for Weights and Measures. This includes time which is a Measure.
So states can not make their own Daylight savings time rules or jump time zones unless Congress allows it.
The current law allows states like Arizona to opt out, but if a State follows DST they can only follow the current approved DST from March to November. So SC can't expand that to year round.
This is good because then every state/region would have their own DST rules and that would be confusing as hell. This way all states are on the same page.
Thank you, excellent reply. Much appreciated.