The data which u send from backend is in "ISO 8601 date" format this has been supported by extjs. This needs to be resolve with help of Ext.Date.format class. Refer below link for your reference.
http://docs.sencha.com/extjs/4.2.0/#!/api/Ext.Date
You need to add 'format' config to datafield and timefield and pass your format as string.
Thanks