Hi
I used to disolve the salt in the water first, and then add the lye.
But a several times I have forgotten to add the salt before the lye, and have thrown it in the warm lyewater after the lye is disolved. No issues with that, it disolved perfectly
(actually much, much faster, because of the warm lyewater) The soap itself hardened up just like it does with salt I have put in cold water first, it did not effect the hardening effect. So now I actually prefer to do it after the lye has disolved.
One time I was adding the salt (1 ts) after everything was mixed at trace. I did it in a small batch of soap and took a chance., The salt grains did not dissolve properly in the mix. It didn`t make any problems in the soap beside I could feel just a few tiny grains that had sunk down, and it was a small batch for a test (300 gr). They melted in the wash so not a big deal, but I prefer to disolve it completely before adding it to the oils.
When I make saltbars of course the point is having you feel the salt in there, but that is a different approach completely.