Join Date: May 2008
Location: Orange County, CA
Programs: AA LT PLT, DL PLT, HH DIA, IHG PLT, Hertz PLT, Bonvoy GLD, Avis Pres Club
Posts: 1,265
cmhua777 is correct.
Clearing customs/passport control upon entry is super easy. US$5 entry fee (cash only), in and out in less than 5 minutes.
The biggest issue is making sure you can get your boarding pass from MGA-MIA in advance of your arrival. The check-in counter at MGA is pitifully slow, even for elites/premium pax. You could easily take 30 minutes in line at MGA ticket counter to get a new boarding pass.
From there you have to go through passport control again before security. This could take up to 15-20 minutes. In any case it's faster than the ticket counter.