Time Zones

The Day Rolled Over and Yesterday's Wallpaper Came Back — Designing Date Boundaries Instead of Trusting an Agent's Time Code

A record of redesigning a daily-rotating wallpaper feature that showed yesterday's pick after midnight for some users and switched twice in one night for travelers. I separate the device clock, time zone, and daylight saving time into three distinct failure sources, show how to define a stable day key, defend reward boundaries against a rewound clock, and test it all with an injectable clock — from a solo indie developer's point of view.