Sunup and sundown are subjective. At "sunset" it's not pitch black out. Is sundown earlier if I'm in a neighborhood behind a hill?

I don't want to have to guess if a business will still open by the time I get there. I know that it's 6:15, it's a 22 minute drive, and the business closes at 7. I have no idea if "sundown" will have happened by the time I get there.