There isn't a timetable for the Caspian Sea ferry. The ferry leaves when it’s full and if weather permits. The best you can do is to head to the ferry port in Alat (75km south of Baku) and to chek-in and get your name entered on the passenger list to be sure to have a place on the next ship leaving (This is also the case if you already bought the ferry ticket online, you need to check-in at the port).