Do I need to start recording the time for all my sessions?

There is no need to use the 'Timer' feature (it's just an option). By default the hours for any appointment you schedule with your clients are automatically added to your Certification Report. Those hours are added to the 'Paid' column within the report. If you need to enter 'Pro Bono' hours, you can choose that 'pro bono' option in the scheduling window when you are scheduling your appointments in your Console calendar.