Arrive 10–15 minutes early for a booked slot.

Unless you’re going to a courthouse or a hospital, 10–15 minutes is plenty. Security checks are usually a 2-minute thing unless there’s a surprise line. Elevators might add another 2–3 minutes if you’re on a high floor.

If you show up 30 minutes early, you’re just standing around looking anxious. That’s not useful to anyone. The only exceptions: federal buildings with metal detectors, or a building where you know the elevator bank is a bottleneck (like a 40-floor office with four elevators). In those cases, go 20 minutes.

Plan for the worst normal day, not the one-in-a-hundred meltdown. If you’re late because of a real delay, call ahead. That’s more professional than hovering in the lobby for 15 minutes.