So in regard to your question I do think you will get greater gain, but I also think you will get burnt out within a few days if you try to get 2 hours of underwater time a day. You will be spending about 4 hours in your pool a day. If you have the time and motivation I say go for it.
-Benny
Alex
Alex
For creativity, not everyone is meant to be creative some have better math skills others language. Not to suggest that you don't find ways to enjoy creative activities. You might find more fun in art, music if you realise you probably already are much more creative than you give yourself credit for.
On the whole I do suggest you focus on one aspect you would like to improve at a time. That way you can see results faster. In all it still comes back to actually spending time using the mental skills you talk of. Considering the brain is like a muscle you need more than one type of exercise to develop it.
In any case your best results will be with the first hour after that diminished returns. Consider also that you are actually depriving your brain of oxygen during that period. Longer periods could be more actually cause the reverse of the desired results, because you're not necessarily challenging the brain instead perhaps damaging it. The problem may not even become noticable for many years.
They say everything in moderation. Exercising any muscle for more than an hour a day, especially in the beginning, causes more problems than it's worth.
Alex