I would like to show a friend the manatees however we can't get there due to work until after the 4 pm closing. Would we be able to walk outside the building and look in the water around 5 pm?

We tried that last year and didn't hear much success. When we came the following year during regular hours it was much more enjoyable

There's a gate that closes after everyone leaves the facility at closing time.

Call them they have a web page

I'm sure There's no gate to block people off

If the building is closed I do not see why they wouldn't let you walk outside and admire the views