The nice thing about shellac is if you don't like it, soak a pad with DNA (I use paper towels and change often) and rub it off. Test some of your shellac on a piece of scrap. It should dry to touch in 15 to 20 minutes. I sand mine at 30 minutes, no problem. If yours is not dry enough to sand in an hour, buy new.
Check the date on your can. Seal Coat should have a 2 year-plus shelf life BUT, shellac will age differently based on how it is stored. High temperature in particular, shortens life per the manufacturer. I keep mine in my office in the house (I figure if I'm happy, its happy) and have never had a problem.
Any sufficiently advanced technology is indistinguishable from magic.
- Arthur C. Clarke