It looks like I will have a long layover in Miami due to some flight cancellations in the fall. Is 6 hours enough to get to South Beach for a late lunch? We arrive at 1:50 pm from Phila and depart to Buenos Aires at 8:30 pm. Is there a checked luggage place or lockers where we can leave carryon?

If we can't go to town, is there a hotel close or attached to the airport where we could get a day rate and get some work done?

No left luggage service or lockers available at the airport.

There is an attached hotel. Nothing special but I'm sure you can negotiate a day rate if the place is not full.

Google "Miami airport" to get info on the hotel.

My experience with Miami Airport and local traffic suggests that you would might be buying into a problem with going to South Beach.

Assuming you are checking luggage through or taking carry-on only, it will take you 10 to 15 minutes to get to the rental car shuttle bus pickup.

From getting to the curb to underway could take as much as a half an hour.

You should be able to get to South Beach in a half an hour, it now would be around 3:00 p.m. (See where I'm going with this?)

With a quick choice of place to eat and an attentive valet parking attendant you could be underway again at 5:00, but by then you can expect an hour drive, at least to get back to the airport car rental return. (The only time I've seen Miami area roads uncrowded has been on the transition shots on CSI Miami. Those are as unrealistic at the rest of the show.) Then it will be at least a half an hour to the Terminal.

I think most of us who have used MIA, would expect at least a half an hour to go through security to get to the gate.

IMHO, it appears you would be better off buying a day entrance to one of the airline clubs or having a meal and a nap at the attached hotel.

Tempting as it is to want to make use of your long layover, going to South Beach isn't an option timewise (ie traffic, getting back to airport on time, clearing security again, etc.).
See where you can do work from within the airport as suggested by Jeff801.

Every time I've been through MIA the security is a nightmare.

I'll ditto the day pass to a lounge suggestion.

Thanks for your detailed responses. It seems you are assuming I would try to rent a car which is not something that I even considered. I assume the answer might be a bit different if we used taxis. Let me know if you think that is the case.

If the attached hotel fitness center and pool reopen perhaps that is an option too.

Miamian here. I have to agree with the other suggestions that you stay at or near the airport.

If the stars align, a cab to and from South Beach and lunch on Ocean Drive or Lincoln Road is perfectly doable. But that's putting a lot of faith in the stars aligning. I'd be most concerned with getting back to the airport. You'll be hitting rush hour going west on 836 or 112 - horrible on a good day but if there's an accident or something you're in trouble. If by chance you're traveling on a weekend, you don't have work rush hour, but you'll have the beach exodus which can even be worse - the MacArthur Causeway crawls heading back to the mainland on weekends. Aside from the cost (cab fare at approx $35-plus each way), I don't think the rushing and worrying would be worth it.

Thanks so much for all the responses. I'll look for a day rate and get some work done. Probably the best option since the flight changes meant more time out of the office anyway.

I was in Miami a couple weeks ago - and even by cab - I would not trust getting back in time for your next flight IF having a nice, relaxing time in South Beach was your goal. I think you're making the right choice. I bought a day pass for the American lounge (happened to be flying American that day), and I was able to relax there....