Jumpseats come and go. Just because one is open an hour before a flight, it doesn't mean that you are going to get it. Depending on how that company operates, it may go to a company employee flying on his own metal before you, or may go to someone on your metal that is more senior to you.
At my company, I have 2 hours to get to the gate while on reserve. I live 30 minutes away, so I sit reserve in my house. I go about my "normal" life, with the exception that I wear work pants with a different shirt, and there is a packed suitcase in my car. Oh, and I can't drink a glass of wine with lunch.