The above page has the monthly schedule at Antaiji. They sit for 4 hours of zazen on regular days while for 15 hours on sesshin days. Below is their typical sesshin day. They spend about 9 days every month in sesshin schedule (every month 1st to 5th is sesshin schedule as well as every 10th, 15th, 20th, 25th). You need to pay nothing to stay there. You can choose to donate (I guess most people do). You are only expected to share the work and follow the rules and stick to the schedule there.
4am to 9am Zazen 9am Breakfast 10am to 3pm Zazen 3pm Lunch 4pm to 9pm Zazen 9pm Lights out