What date field does Telligent use to sort by date?

The date in search is the creation date of the thread (most indexed items' dates are their creation date). Instead of using search, I'd recommend using the thread list API:

Specifically something like:

/api.ashx/v2/groups/[GROUPID]/forums/threads.xml?ForumThreadQueryType=Answered&SortBy=LastPost&SortOrder=Descending&PageIndex=0&PageSize=3&IncludeQuestions=true&IncludeDiscussions=false

Thanks Ben for the information. We will try the API you provided.

Regarding the Date, We want to know what date you use for sorting all the Threads and wiki page.

For threads you mentioned it is the creation date, is it the same for other content types too. 

I was identifying the date stored for date sorting in the search index. When working with individual types (not in search), it's possible to search on other fields as well (including other dates).

I was identifying the date stored for date sorting in the search index. When working with individual types (not in search), it's possible to search on other fields as well (including other dates).