There is usually no problems in leaving the airport for layovers. In fact, being a smoker I do it all the time, whether I stay on the airport grounds or go to a hotel. You might have to pick up your luggage though, just inquire with your airline what the situation is. Usually, if your itinerary is booked all on one ticket or reservation number and with the same airline then they will transfer it automatically. You will have to go through the security process when you return to get your flight to Guatemala (and possibly re-check in your luggage).