Be careful. The AC in Miami is behind the security gate and the lines are horrific most hours of the day. It might not be worth it to go to the AC if the layover is only 90 minutes. It's your call but every time I'm in Miami the lines are horrible, the security staff is horrible, everything is horrible. However, the AC staff is good there.

Good luck.

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Have fun today because tomorrow you may regret not enjoying yesterday...