I'd say the worst case to get from a gate in the A concourse to a gate in the C concourse is about 17 minutes at a walking pace. Figure about 7 minutes worst case to get to the center of A concourse (using tram when near ends). The tunnel is about 1/4 mile = 5 more minutes. Finally, the last gate on the C concourse is about another 1/4 mile = 5 more minutes.