If you are arriving at TBIT on an international flight and have to clear immigration and customs, you will be outside the secured area when you exit the Federal Services Inspection Facility and it will be quicker to walk outside, preferably on the upper level (the lower level is semi-covered, is noisy and has lots of exhaust fumes and second-hand cigarette smoke); it's about a 15-20 minutes walk. If you are airside at TBIT, because the airside route is not as direct, that walk will take a few minutes longer. Here is a link to a map.