For our last several trips, we've only returned thru MIA usually on the morning flt from SXM on a Thu or Fri. Had 3 hr layovers and usually took about 45 mins to clear customs and immigration each time. Have read comments from other TTOL folks about Charlotte indicating sometimes its great but other times not so much (long waits on tarmac or not enough personnel manning the customs and immigration lines). Suspect its all about which day and at what time you'll be traveling thru.