The walk inside TBIT is longer than the walk from TBIT to T4 (it is about 50 m between buidlings and maybe 100m door-to-door). The issue is the security screening time which varies hugely by time of day (AA T4 has highly clustered flight scheduling, so there is a lot of pax 6am to 9am and then again at 10pm, with long lines at times). Being able to use priority lane makes a big difference.