Sort By Ascending/Descending Date/Time Forum Thread Post in Smart Search Filter from Smart Search Re

I'm trying to create a Smart Search Filter that will sort the results of forum posts by date/time. I would like to create a radio button or checkbox that says @Ascending@ and @Descending@ which will sort the queried results according to date created. In the Values field of the filter, I'm not sure how to fetch the date/time data of the forum results. Is it by classname? Could anyone shed some light on this?