I've never been the litigious type Ian, but where this is issue is concerned I would be mightily tempted.
It's all about the frustration you see.
I am sure that deep within the terms and conditions of membership there will be a clause about 'Management reserve the right to amend opening times or 'the offer' or suchlike.
To me, the issue is more about how keen they are to gather new members, and get new subscriptions in to the coffers.
When you ask the question about Pool usage, they always say that there is 'no problem' or 'it's unlimited'.
The reality kicks in when you study the colourful timetable leaflet in detail, or worse, actually turn up clutching your swimming cossie, eager to use the membership that you so extravagantly pay for.