> there is no difference between local time and "offset from UTC"
The difference is between applying the UTC offset for a future event using present rules. What we are saying is you should not do that because the rules can change.
I ask you today that we meet at 3PM on January 24th in 2026, at the train station in Berlin.
In my paper calendar book for
I mark the date January 24th 2026 with the following note: “meet jvanderbot at 3PM at the train station in Berlin”.
I carry this book with me for the next few years.
Meanwhile, you decide to be modern so you store a note about the meeting in a database. In doing so, you convert the information into a UTC offset for that future time. But you are using current rules for today, which may change.
And then when the day arrives, there has been political changes in the meantime that made it so that the utc offset is different.
Because you converted to utc offset ahead of time, your representation of the time no longer maps to “3 PM” but instead to let’s say “4 PM”.
I show up at 3 PM local time, as we had agreed. But you are nowhere to be seen because in your digital calendar the meeting appears to be for “4 PM”.
This is what we mean when we are talking about the problem with converting a local time to a UTC offset a long time ahead.
The difference is between applying the UTC offset for a future event using present rules. What we are saying is you should not do that because the rules can change.
I ask you today that we meet at 3PM on January 24th in 2026, at the train station in Berlin.
In my paper calendar book for I mark the date January 24th 2026 with the following note: “meet jvanderbot at 3PM at the train station in Berlin”.
I carry this book with me for the next few years.
Meanwhile, you decide to be modern so you store a note about the meeting in a database. In doing so, you convert the information into a UTC offset for that future time. But you are using current rules for today, which may change.
And then when the day arrives, there has been political changes in the meantime that made it so that the utc offset is different.
Because you converted to utc offset ahead of time, your representation of the time no longer maps to “3 PM” but instead to let’s say “4 PM”.
I show up at 3 PM local time, as we had agreed. But you are nowhere to be seen because in your digital calendar the meeting appears to be for “4 PM”.
This is what we mean when we are talking about the problem with converting a local time to a UTC offset a long time ahead.