I don't follow exactly. The duration of the tasks vary or do the start and finish of the tasks vary. I would suggest the following. Express the duration in days where 1 day = 8 hours. You can define multiple calendars with the different working configurations. Then add the task calendar column and change the task calendar to reflect which "shift" is going to perform the task. The duration will stay the same but the finish date will change depending upon the definition of the calendar.