We set off from Miami around 9.30, did a boat tour on route 41, then headed back around lunch time down the 997 to route 1, got to Key West around 5, so plenty of time depending on how long you want to stay but also depends on which part of Everglades you want to be in. Careful to check out the tour reviews on boat rides, we went with Gator Park (I think) as it wasn’t too far along the road but it was a bit naff.
Don't forget the insect repellent. Mosquitoes are terrible in the Everglades.
Go to Route 41 only if the airboat thing is important. Being on an airboat is NOT the way to see the Everglades. You are traveling too fast to see anything and you scare the wildlife. If your final destination is Key West, there is really no reason to go out to route 41. It's out of the way.
On your way to Key West, you can easily stop at the Anhinga Trail, which, in my opinion is the best place in all of Everglades National Park to see gators, turtles, birds and all different kinds of wildlife. It's a paved walkway through the middle of the Everglades that makes it super easy to stop, take photos and take in the beauty of Florida's gorgeous eco-system. Forget the airboat.
I agree, the Anhinga trail at the south entrance offers the most wildlife viewing for the least detour. You make a right immediately after the Turnpike ends, at the traffic signal right where the Turnpike ends and you merge into US-1 in Florida City. It takes maybe 20 minutes from Where you make the right to the park entrance (you can stop at the Ernest Coe visitor center to learn about the area and get a free map) and another 10 mins max to the anhinga trail. It's a boardwalk raised about 6ft above the water and maybe 3/4 mile long. The only problem might be the recent weather we've had (I think you arrive in about 10 days). It's rained non-stop so firstly the mosquitos may be quite bad for this time of year and secondly the wildlife does disperse through the Everglades far more when the water level is higher. When it's been dry the wildlife all congregates at places like the Anhinga trail as there's always water there. You could call the park a day or 2 before and ask how bad the mosquitos are and also if there's many gators and wildlife there right now. They usually give pretty honest advice as they don't want everyone to visit and be miserable. We've seen zero alligators one time and been literally tripping over them on the path on a different visit.
If the mosquitoes aren't bad you can drive on a few more miles and walk pay-he-okee trail just to see a different aspect of the Everglades. Unless you have a really keen interest then that would probably be your Everglades itch scratched. If you venture off on the other trails you'll drive much further and they are more dense with vegetation, and therefore mosquitos.
There is an airboat ride at the Everglades Alligator farm, which is on the way to the Anhinga trail, but I think it's only available as an add on to the gator park admission. As mentioned, the other airboat rides are up on Us41/Tamiami Trail, which is more of a detour to the west from the airport. It is a little bit of a drive down 41 to get to the airboat rides. The route from there down Krome/997 down to the Keys mentioned by northerner1974 isn't a bad one as you skip the busy area of the Turnpike around Miami. It can be slow going though, but no more slow than rush hour on the Turnpike usually. Just depends on your timing. You'll spend a lot more time detouring to 41 than popping in to check out the Anhinga trail I'd say. Depends how set on an airboat ride you are. If you land early enough and are in no hurry do both.
When are you visiting?
I wouldn't want to tour the Everglades in the warm months. We once spent several hours driving around, stopping at different places, but this was on our last day in the Keys, and we were spending the night by MIA, so no hurry.
But since it was in January we didn't encounter any mosquitoes.
Thanks very much for the superb informative responses.
We arrive June 1st can’t wait...