If you want to set a datatime field in MS CRM 2011, you can follow below code for the same
//Set current Datetime field in Javascript
var _D=new Date();
Xrm.Page.getAttribute(‘fieldname’).setValue(_D);
//Set Current datetime in Server side code
DateTime _CurrentDate=DateTime.Now;
_EntityObject[“AttributeName”]=_CurrentDate;
//Set retrieved date using Rest
var _DateVal = dateReviver(Resultset.DateAttribute); //dateReviver is a function to format date
Xrm.Page.getAttribute(“targeAttributeName”).setValue(_DateVal);
Enjoy!!!