Do they do it “all the time”?
Yes, all of mine do. Especially for common property areas where a resident or owner shouldn’t ordinarily need to be.
But this is about an OC provided recreational facility. Setting the hours of operation and even a season is commonly done by OCs. I think it would be likely that a Tribunal would agree that the OC itself gets to decide them. And even to remove the facility altogether if it so voted. I know of OCs that have done that.
Comparing it to car park access is not really the same thing. And if the parking space is on title, as is now the norm, an OC must provide 24/7 access to it.
I can’t see how setting the hours of operation of a recreational facility could be considered as “altering common property”.