How to insert item into list in order?

I have a List of DateTimeOffset objects, and I want to insert new ones into the list in order.

List<DateTimeOffset> TimeList = ...
// determine the order before insert or add the new item

Sorry, need to update my question.

List<customizedClass> ItemList = ...
//customizedClass contains DateTimeOffset object and other strings, int, etc.

ItemList.Sort();    // this won't work until set data comparison with DateTimeOffset
ItemList.OrderBy(); // this won't work until set data comparison with DateTimeOffset

Also, how to put DateTimeOffset as the parameter of .OrderBy()?

I have also tried:

ItemList = from s in ItemList
           orderby s.PublishDate descending    // .PublishDate is type DateTime
           select s;

However, it returns this error message,

Cannot implicitly convert type 'System.Linq.IOrderedEnumerable' to 'System.Collections.Gerneric.List'. An explicit conversion exist (are you missing a cast?)