#1175·winmerge

Daylight Savings Time (DST) causes exactly 1 hour difference on FAT

Author: MM-JohnCreated Feb 2, 2022Updated Aug 30, 2026
Labelsenhancementfolder compare/merge

When comparing to a USB flash drive in FAT or exFAT formats the time is reported as exactly 1 hour different on Windows because of time interpretation and Daylight Savings Time (DST). There's no workaround. If you manually change all the times on the USB drive then next DST change it appears wrong again. You'd need to change all the times on all your files in FAT twice a year.

Similar to the "Ignore time differences less than 3 seconds" option, can there be a "Ignore time differences of exactly 1 hour".

However, it's complicated, because it's probably 1hour+/-3 seconds. Ie both options combined together. Not totally sure of this.

For reference, the Eastern Standard Time (EST) changes to Eastern Daylight Time (EDT) in the summer in the USA (northern hemisphere).

Here is a similar discussion in a tool with similar comparison needs - FastCopy - for reference:

"Daylight Saving Time DST" problem (= "1 hour exact difference" problem) https://groups.google.com/g/fastcopy-bb-eng/c/0ovpgsRc66E/m/ItX7q7-yAQAJ

Is the DST problem fixed in FastCopy v. 3.40? https://groups.google.com/g/fastcopy-bb-eng/c/IAitTRfFojY/m/woRXcWvgCAAJ