> just use UTC on day one, regardless of requirements That can cause extra concerns for always-in-one-timezone systems where you might care where midnight fall

> just use UTC on day one, regardless of requirements That can cause extra concerns for always-in-one-timezone systems where you might care where midnight falls (“did this event happen today or yesterday?” is a question that needs extra steps to answer, for instance). Nothing complicated, but extra work you might want to skip at the quick PoC stage. But yes, beyond PoC work and all but the simplest other work, I'd agree with UTC all the way from the ground up.