> OK so I set up a user field as original date/time.
TP9 databases already have an "Original Date/Time" userfield by default. You don't have to make one yourself.
Click on the lightbulb icon above the thumbnail listing to enable its display in the thumbnail listing. Then click on the pull-down menu to its right to set the primary sort order to that user field.
(Alternatively, you can use Modify File Info (Ctrl-Shft-Q) to set the timestamp of your files to their embedded exif time stamp, and then sort on the regular filedate. That's probably a bit faster and it doesn't require you to display the Original Date/Time user field value)