|See FileSystemInfo.LastWriteTime Property (System.IO)[^]:
Quote:Note This method may return an inaccurate value, because it uses native functions whose values may not be continuously updated by the operating system.
The value of the LastWriteTime property is pre-cached if the current instance of the FileSystemInfo object was returned from any of the following DirectoryInfo methods:
To get the latest value, call the Refresh[^] method.
So you might get an old time stamp especially when the file has just been updated.