you mean to take off the "mother" that surrounds the
seeds right? Well it only takes about a day or two. If you go longer than that the
seeds will sprout. Ask me now I know lol. Yep I did off season tomatoes one year because I left the
seeds in the vinegar and water solution to long.
I've actually found that drying them and then storing them in paper
seed packets works just fine. But they so stick together so I have to pull them apart by hand if I dry them. For me that's no problem because I have lots and lots of time. But, most people are busier than I am.
Good luck with your
seeds.