On the desktop show the same attribute twice. Once for the picking of the Date and one for setting the time. For time there are a couple of widgets in the appstore:
Timeinput https://marketplace.mendix.com/link/component/113044
jQueryUI Datepicker and Timepicker https://marketplace.mendix.com/link/component/106243
Simple Time Widget https://marketplace.mendix.com/link/component/111601
Regards,
Ronald