Did you try cboxHour.Items.Clear()?
If you just want to clear the current selection, but leave all of the items in the list, you can use:
cboxHour.SelectedIndex = -1
How do I clear a combobox?
Did you try cboxHour.Items.Clear()?
If you just want to clear the current selection, but leave all of the items in the list, you can use:
cboxHour.SelectedIndex = -1