Lunch hours to be deducted from Full Day

Summary:

Default working hours for my technicians eight hours per day.Let’s say the technician is supposed to complete a internal activity for the day which is of eight hours duration. However there has to be one of our lunch break for the technician. Think start time is 8:30 am and time 5:30 pm with the lunchtime of one hour which is from 12 pm to 1 pm. How can Technician start his activity in such a way that only eight hours is considered as a duration for the activity?