Fix time slider to range 0-24 instead of 0-12,0-12

In the timepicker widget, as of version 1.1 and above (RT upgraded to
1.2 in a3de102), a format of "hh" is 12-hour time, not 24-hour time.
This caused the value inserted by the slider to only range from 0-12.
Properly insert 24-hour times by using "HH" in the format instead of
"hh".
Merge branch '4.2/timepicker-24h'