Look for some input widgets in your mainwindow_ui File. First make a QT Project u need QT4-GUIApplication
QTimeEdit or QDateTimeEdit and search for the member Functions, if they provide what u need. If not, you can try to subclass them and build your own functionality. See @ Forum, Wiki, Tutorials, Books, etc...

http://doc.trolltech.com/4.5/qtimeedit.html or
http://doc.trolltech.com/4.6/qtimeedit.html depending wich QT you are using..

greetz A.