I am not sure I understand what you want to do? From what I gather you want to store the date at which the #fav column is changed for sorting purposes?
- if the #fav column is exclusively updated from the Action Chains plugin, the best solution is to add another action to the the same chain that updates a custom date column together with the #fav column
- otherwise, you can use the Last Modified plugin. You also need a custom date column for this.