Remember that dates are stored as a Dual values in QlikView. They are numbers with a text representation. Marco's advice showed how to set the text representation the way you wanted it but the number is not rounded to the hour. So when you later went to make a bar chart you find that because QlikView still stores the time with a precision of minutes you're getting the bar chart as shown.
Wrapping Text() around your time dimension in your chart should give the result your looking for.
You've asked another question here after Marco had answered. I suggest that it would be fair for you to mark this question as having been answered by Marco.