Usually drink service starts as soon as captain allows cabin crew to get up, about 30-40 minutes after take off. Then meal service in courses even late night. The menu for the evening should be handed to you at your seat, while Y class is boarding. Take a look and pick what you want--you don't have to accept all the courses, or even any of the meal. I should think for an F passenger, they can be more flexible about what/when/how you are served. Haven't done BKK-ZRH but have done the overnight BKK-FRA and I think there are 2 meal services (+ snacks available in the galley midflight). Usually the 2nd service is the smaller/simpler of the two. But others should comment here, as my experience was about 3 years ago on the European route and TG may have changed things.