Plus...
...I don't think that the length of the bath matters too much...because of the nature of osmosis.
In the molecular transfer through the tiny openings in the skin, water will balance the salts (all substances) to be equal on either side.
The water WITHIN the cells contains exactly the right amount of all salts, else we wouldn't be alive. That's how smart are our bodies.
It's the water AROUND the cells that varies...and what we affect with bathing.
If we can bathe in water containing the closest approximation to 'perfect' mineral balance we can get our hands on, one percent (1%) solution, at 97 degrees, for 20 to 30 minutes, it won't matter much if we should stay in for, say, 40 minutes. The solution can't put MORE in, because we have already reached the most balance that bath can give us.
Add more water, and the body fluids around the cells will change to a more watery (less than 1%) salts solution...which is undesirable.
Also, 97 degree bath may feel somewhat cool, but so does all swimming water, until we get 'used to it'.
Another thing...I suspect that this good-salt bath might help with weight loss, too, diluting out substances the body doesn't need/want. Hoping. ;)
F.