Once you have made changes in a day's working times, either by setting a vacation day or by setting special working hours, in the calendar, the color of the day changes, indicating that it has been changed. You may wish to copy this day's working hours to some other days as well. To do this, in the user time editing dialog:
Click the Copy selected day button
Click on a different day to select it
Click on the Paste to selected day button. The copied day's working hours are copied to the new day.
In an analogous fashion you can use the Copy selected week and Paste to selected week buttons (the selected week is the week that the selected day belongs to).