It's simple model for calc time in work hours for 2 main methods

1. AddWorkTime - add time in work hour. Calc end time of planned task.
2. DiffWorkTime - calc total time in work hours of task.

Work calendar has default settings for work week, that can be overwitten. For overwrite day, just add them into calendar and set type of day and worktime of it. Day can contain many work periods.

• TimeSpan defaulStart -- Start of work day. Default 8-30
• TimeSpan dafaultEnd -- End of work day. Default 17-30
• TimeSpan dafaultShortEnd -- End of short day. Default 16-30

• Workday -working day
• ShortDay -working day
• Weekend -not working day
• Holiday -not working day

• WCDayType monday -- Default Workday.
• WCDayType tuesday -- Default Workday.
• WCDayType wednesday -- Default Workday.
• WCDayType thursday -- Default Workday.
• WCDayType friday -- Default ShortDay.
• WCDayType saturday -- Default Weekend.
• WCDayType sunday -- Default Weekend.

WCalendar wc = new WCalendar();
//add an a holliday
//we can add a title for day for next using it in calendar
wc.days.Add(new WCDay{
  dayType = WCDayType.Holiday,
  title = "Happy new year",
  date = new DateTime(2020, 1, 1)
});
//set 2020/12/31 as short day
wc.days.Add(new WCDay{
  dayType = WCDayType.Workday,
  date = new DateTime(2020, 12,31),
  workTimes = new List<WCWorkTime>()
      {
           new WCWorkTime(new TimeSpan(8,30,0),new TimeSpan(12,30,0))
      ;
});

\\calc en date
DateTime endDate = wc.AddWorkTime(new DateTime(2020, 1, 20, 12, 47, 0),new TimeSpan(16,0,0));
\\calc result time 
TimeSpan totalTime = wc.DiffWorkTime(new DateTime(2020, 1, 20, 12, 47, 0),new DateTime(2020, 3, 10, 18, 12, 0));