Here is a test doc:
Sample-OPML-export.tbx (110.3 KB)
To export the OPML, select the ‘Export Agent’ in the view pane, then use menu File ▸ Export Selected Note. Save the resulting file.
In OmniOutliner, use menu File ▸ Open, and locate you OPML file to open it in OmniOutliner. Now, open menu File, press the Option key so the ‘Duplicate’ option in the menu changes to ‘Save As’. Click that and in the save dialog, choose OmniOutliner format.
Now you have a proper OmniOutliner file, for the column head for each date column you can right-click the header and choose Format ▸ Date.
Sorry if that’s complicated but the limitation is in the OmniOutliner app rather than Tinderbox.
Here is a ZIP file holding the above TBX, the exported OPML file as created by Tinderbox and the same imported to OmniOutliner and saved as an OmniOutliner-format file with the date column data types set (as above).
Sample-OPML-export.zip (63.1 KB)
Sorry for the delay. I don’t recall the OmniOutliner end being so complicated in older version of the app, but it’s a good example of apps not giving thought to data input from file. 