Is there a way to create a TimeEntryItem for another user? I can persist the 'User' field before creating a new TimeEntryItem and see the User information being passed to Rally, but so far I get the following warning in the response, and the create request is treated as being for the calling user...
Warnings:["Ignored JSON element TimeEntryItem.User during processing of this request."]
I don't think this is currently possible via the api. The warning you are getting above indicates that the User field is not writable, even on initial creation. So it is always just populated with the value of the current user making the request.