Daylight Saving Time (DST) shifts clocks forward (usually by one hour) during part of the year. The goal is to extend daylight into the evening in warmer months. However, DST is not universal and can create confusion for international coordination.
Different countries start and end DST on different dates—or may not observe it at all. As a result, the time difference between two cities can change during the year, even if both use DST.
DST is a policy choice, not a natural rule. Treat it as a variable that can change and verify it when planning ahead.