Why a Meeting Time Looked Right But Was Actually an Hour Off
This typically happens when two regions observe daylight saving time but switch on different calendar dates — for a period of a few weeks each spring and fall, the usual time difference between those two zones shifts by an hour compared to the rest of the year, catching a conversion calculated from an outdated or generic offset.
This specific, recurring scheduling error affects a surprising number of cross-border meetings every year, and it has a precise, identifiable cause rather than being random bad luck.
Why the offset isn't constant year-round
Many countries observe daylight saving time, but they don't all start and end it on the same calendar date — the US and the EU, for example, transition on different Sundays in spring and fall. During the window between one region's transition and the other's, the usual time difference between them is temporarily one hour different than it is the rest of the year.
How this actually causes an error
Someone who mentally memorizes "London is 5 hours ahead of New York" and applies that fixed offset year-round will be correct most of the year, but wrong during the transition window when only one of the two regions has switched — leading to a meeting that lands an hour early or late relative to what was intended.
How to avoid this specific mistake
Rather than memorizing a fixed offset between two zones, using a tool that calculates the conversion for the specific actual date of the meeting accounts for daylight saving transitions automatically — this is exactly the gap that causes the error when done from memory instead.