What if the date for DST changes tomorrow, but only in some locations? How will you know which stores times need to be adjusted and which don't?
UTC to local time is not a function, it is not somethung that can be computed once and stored for the future. The two are fundamentally different concepts, and can only be related to one another in certain contexts, and only reliably for the past.
> How will you know which stores times need to be adjusted and which don't?
There are a number of libraries for this, usually updated by the unpaid volunteer in Nebraska. Or else your company has staff whose job it is to follow this for any place you operate.
If you record opening times as UTC, well, then you have to change to UTC when the store switches standard <=> daylight.
This is what Fred Brooks called an essential complexity. You can poke the pain from one part of your system to another part, but it's never going away.
The function is complicated. There is no avoiding that.
One Pacific island nation duplicated a calendar day when it switched International Dateline sides to more closely align with Australia instead of Hawaii, reflecting a shift in its economic ties. No idea how they handled it exactly but pretty hairy to model.
UTC to local time is not a function, it is not somethung that can be computed once and stored for the future. The two are fundamentally different concepts, and can only be related to one another in certain contexts, and only reliably for the past.