I think you are looking instead for a WeeklyTrigger. The following code will run the action every week on weekdays at the specified time.
td.Triggers.Add(new WeeklyTrigger(DaysOfTheWeek.Monday | DaysOfTheWeek.Tuesday | DaysOfTheWeek.Wednesday |
DaysOfTheWeek.Thursday | DaysOfTheWeek.Friday) { StartBoundary = dtCalendar.Value+dtTime.Value.TimeOfDay });