Is it possible to leave the nap in the basic soup for too long?

I don't think so. The solvent can only hold so much. After it has reached full saturation regardless of how long it stays in the basic solution it cannot hold any more alkaloids.

Thats what I thought but wanted to double check.

Not at all, If I know there's some alkaloids left over in a mix and I want to grab the last remaining bits, I'll often put 50ml in mixing it as you would a normal pull then leave it for 24 or more hours until I get back to it. I'll just mix it as I remember to and then decant when ready. Never had a problem doing that.

As Concombres said It can only hold so much before fresh solvent needs to be introduced.