According to the Excel Rendering Design Considerations article:
- The "f" DateTime format string should result in a full date/time pattern with a short time pattern.
- The "F" DateTime format string should result in a full date/time pattern with a long time pattern.
After exporting to XLS/XLSX, the time formats are as follows:
- "f" -> full date/time pattern with a long time pattern.
- "F" -> full date/time pattern with a short time pattern.