If you have a technician coming in later or earlier than their default schedule is set (default schedule is set on the Employees Availability Tab), you can make an adjustment to their schedule for a single day, from Employees > Scheduling > Schedule.
Select the date. Double click on the employees name from the schedule. Adjust their start time or end time accordingly. Keep their Out Code Status set to Available. This way they'll be able to clock in/out and check in/out of the jobs their working during the shortened availability for that day.