You can use the 'Date Added' column to sort your items based on the time you added them into Tropy; you cannot modify this property as it is set automatically.
You can use the 'Date' / dc:date column (or any other column) to sort by dates you assign yourself. At the moment Tropy supports only string values, but will support more types, including dates in the future. For the date field in particular, it is best to record your values using the ISO standard (including the upcoming extended format). Here are a couple of examples for normal dates:
Or for uncertain/approximate dates:
If you record dates in ISO you can be sure that Tropy will convert them properly into real date values once we add support for them; additionally, since all values are currently sorted as strings, using ISO format for dates generally gives you the correct chronological order.