Question: Is there a extjs based datetimepicker?

I want user can select date and time together.

Answer: 
Check out Saki's DateTimeField: at <http://www.extjs.eu/>

"Combined Date and Time Field for applications where entering both date and time is required. Suitable also as Grid Editor. Contains renderer directly usable by grids."
There's also [this one](http://www.sencha.com/forum/showthread.php?137242-Ext.ux.DateTimeField-DateTimePicker-for-ext4-also-DateTimeMenu-TimePickerField), works in ExtJS 4.1, but uses number spinners for selecting time, can be reworked relatively easily to use the built-in time picker.