We went into the Tabacon Hot springs at 10am (when it opened). We purchased the full day pass including lunch and dinner. The first few hours were really quiet and then the families turned up. The spa is a massive area though and there's a section just for adults, so it's easy to get away from the crowd. There's a few swimming pools near the entrance with a slide and swim-up bar. Warning: the drinks are priced three times more than everywhere else.
Overall the spa was beautiful, set amongst the jungle with waterfalls and delicious food. We met up with an American couple we met a few days ago and celebrated in the new year by getting wasted with them. We had a really good time, that's all we will say :-).