>your blood pressure WILL NOT be affected for a very long time //

I was confused but I think you mean "your blood pressure will only be affected for a short time".

You can parse what you said that way but your expression more readily reads [to me, an en-gb native] as saying that blood pressure changes will only appear a long time after salt intake.

I've read that salt has an almost immediate effect on blood pressure and so is used in some emergency treatments to increase blood pressure rapidly. I'd no idea of the mechanism of it though so the hint in 2) is welcome, thanks.