do you think it is safe for them to play outside in an enclosure for an hour or so, if we are watching them?
If by "watching them" you mean being inside the enclosure with them then it is probably safe. They may try to escape to the yard if you have to open a door to go in or out of the enclosure. I have had gliders bolt out of the tent when the zipper was opened far enough just so I could reach out for the TV remote.
Since their active hours are after dark, you would need to be in the enclosure to see them well. If there are bright lights turned on in order for you to observe them, it is likely that they will just find a spot they consider to be secure and remain still or try to hide.
In addition to the heat, you may not want them out if you have mosquitos in abundance as is often the case in Miami. (I grew up there)
Using the plastic mesh and PVC Pipe frame that many folks make cages with may not be suitable for outdoor use. The 1/2 inch openings on the mesh would not keep mosquitos out. The whole cage may be too light weight to keep it from blowing over.
You may be able to cover a frame with Pet Screen to keep mosquitos out.
I would make sure their enclosure is attached to the concrete slab or at least anchored somehow so it cannot blow or tip over.
You would need to check the enclosure very carefully before each use to make sure other animals do not make holes in it during the day that gliders might use to escape at night. I have had field mice, squirrels and a possum rip holes in my patio screen to get in side the porch.
I would make sure that I could reach all areas of the interior of the structure so that I would be able to retrieve the gliders to put them into a zippered pouch for safe transport back into the house after play time