You can choose your pass start date when purchasing your pass. Alternatively, your pass will start automatically by using the first tour or activity. Keep in mind that the Istanbul Tourist Pass only counts calendar days, not 24-hour intervals. For example, if you begin using a 3-day pass on Friday at 4:00 p.m., your pass will expire on Sunday at 11:59 p.m., rather than Monday at 4:00 p.m. As a result, they recommend that you start your pass on the first full day of your trip to Istanbul to get the most out of your pass.