Can you share your time format?
We tried to store time like "2013-11-12T18:14:43+0530" and declared time_stamp as string in fixed schema model working fine.
The time stored in sql server is stored as a datetime type and an example value is :-
The rails plugin model just has the following line in the associated class:-
attr_accessible :mydatetime, :field2, :field3 ....
The corresponding model in the rhodes client app is defined as :-
property :mydatetime , :datetime
property :field2 , :string
property :field3 , :string