Concert tickets list three different times and none of them is "when you should leave the house." Doors, opener, headliner: each is its own deadline depending on what kind of night you're after. Ready Time works backward from the one you actually care about, so the night starts at the show, not in the parking garage.
Doors at 7 means the line formed at 6. The opener "starts at 8" but might walk out at 8:20. The headliner goes on somewhere between 9 and 10, and that time is rarely printed on your ticket. Meanwhile your side of the night is dinner, the drive, a parking garage two blocks away, and a security line that snakes. The venue's schedule is out of your hands, so the only part worth planning is yours.
Plan on arriving about an hour before the printed start time. That covers parking, the security line, and finding your seat with a little room left over. If it's a general-admission floor and you want the rail, your deadline is doors instead, and for a show you care about the plan starts mid-afternoon. Assigned seats give you slack: aim to be seated 15 minutes before the opener, or about 45 minutes before the headliner if you're skipping the opener on purpose. The plan below has a preset for each. Pick the one that matches your ticket, then tap in your own dinner, drive, and parking times. Eating a real dinner first is part of the plan, because $18 venue chicken tenders are not.
Arrive by 6 for a 7:00 start. That leaves 30 minutes for parking and the security line and still puts you in your seat before the lights go down. Check whether 7:00 is doors or showtime first, because the two are usually an hour apart and the ticket doesn't always say which one it's printing.
Yes, and plenty of people do. The catch is that you're guessing when the headliner actually starts. Openers usually play 30 to 45 minutes, and there's another 15 to 30 minutes of changeover after that. If the show is billed at 8:00, arriving around 8:45 is the common bet. It works cleanly with assigned seats and it's a gamble on a general-admission floor, where the spot you wanted is gone by then.
Start with the venue's own event page, which usually lists doors and showtime even when the ticket doesn't. Bigger venues post the night's running order to their Instagram story the day of the show. setlist.fm shows what the tour has been playing at recent stops, which is a decent guide to how long the opener runs. If none of that turns anything up, the box office will tell you over the phone. Then assume the whole thing runs 15 minutes late anyway.
Work backward from the door time you actually care about instead of the printed showtime. For a general-admission floor spot that's doors; for assigned seats it's roughly 45 minutes before the headliner. Then subtract parking, the security line, and the walk from wherever you actually found parking. If you're taking transit, the number to pad is the transfer, not the garage. Venues run late and openers commonly slip 15 to 30 minutes, but that isn't slack you can count on.