Miami does not have an observation deck. No building in the city offers one, and the first genuine attempt — a platform around 850ft up a proposed 90-storey Delano tower — exists as a rendering with no opening date.
What Miami has is a Ferris wheel, and it's worth being precise about the difference, because the two get sold as though they're the same product.
What a wheel is and isn't
Skyviews rises 200ft over Bayside Marketplace in an enclosed, air-conditioned gondola, and the whole thing takes twelve to fifteen minutes of continuous slow rotation. You don't stop at the top. You can't walk around, change your angle, or wait out a cloud. You get the view your gondola gives you, at the speed the wheel decides.
That's a fine thing to do — it's just not a deck, and if you're planning an evening around lingering above the city, this isn't it.
The glass-bottom VIP gondola is the nearest Miami gets to a glass-floor moment, at roughly double the standard fare.
Time it, and ignore one persistent myth
Ride within half an hour of sunset and one rotation buys you daylight on the way up and the Brickell skyline lit on the way round. Biscayne Bay, the PortMiami cruise berths and the causeways all read well from up there; the city does not, particularly, because 200ft is not very high.
One thing to ignore: listings for a "Miami Tower observation deck". Miami Tower's public space is an office amenity terrace a few floors up, nowhere near the top, and it is not a viewpoint. The tower's fame is its programmable exterior lighting, which you look at from the street.