You can create a specific filter if you want to reduce or broaden the default fields you get returned for each question. The field in that list marked with a green check mark are delivered by default. To also have the date a post was created you only have to add a new property to the Question
datacontract.
[DataMember]
public string creation_date { get; set; }
You might want to try a DateTime
there but if the serializer doesn't accept that do the parsing of that creation_date yourself. On Stack Overflow you'll find plenty of examples how to so that.