Question: Is there a extjs based datetimepicker?

I want user can select date and time together.

Answer: 
Unfortunately there ***is not*** a DateTimePicker out of the box, but there are two separate components named `TimeField` and `DateField` that can be used in conjunction to get the functionality you desire.

If you'd rather use Saki's `DateTime` user extension, take a look at [DateTime Field](http://www.sencha.com/forum/showthread.php?22661-new-version-DateTime-Field). The class comments describe DateTime as "[a] combination of DateField and TimeField", so nothing too crazy is going on if you'd like to create your own unique version.
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."