That "dry until it no longer smells of alcohol" tip is the real test, but man, it's brutal. I've stood there like an idiot sniffing a table for what feels like forever. Setting a timer is the only thing that saves me from myself, because my brain will try to convince me it's fine after 20 minutes. It's never fine after 20 minutes.
An old timer at the hardware store told me shellac needs patience above all. He said each coat should dry until it no longer smells of alcohol, which can take hours in damp weather. Rushing it makes the finish brittle and prone to cracking. Setting a timer is a smart way to enforce that wait.