I can't seem to find the magic keystrokes to make it happen. I'm using RestSharp in a .NET application if that makes a difference, but I'll be happy to know for now if it's even possible. If not, I can always pull the exact details for each project one at a time if I have to.
(I work at Asana)
By default, sub-objects and objects returned from queries are returned in compact form, which usually means just the name and id. You can specify the fields you want using the opt_fields option to your query. See https://asana.com/developers/documentation/getting-started/input-output-options for more info.
In your case, try adding the query parameter opt_fields=created_at.