Well, in fact G (daily) means that the bus operates from Monday to Sunday including holidays.
But because you are going to travel on the August 15, buses might not follow precisely the timetable. However, so far Sita Sud company hasn’t pubblished any announcement for the August 15.
Anyway, in order to be on the safe side, you can ask drivers in Amalfi if the bus operates on the specific time and when it comes back (if you are returning to Amalfi)
Have a safe trip!