In 2026, the standard "entry window" for an airport lounge is 3 hours before your scheduled departure time. This rule is strictly enforced by programs like Priority Pass and major airlines (Delta Sky Club, United Club) to prevent overcrowding. If you arrive 5 hours early, the front desk will likely ask you to return later. However, there are two "high-value" exceptions: first, if you are in transit (connecting) between two flights, you can usually stay in the lounge for the entire duration of your layover, even if it's 6+ hours. Second, some premium "First Class" lounges (like the Lufthansa First Class Terminal) allow all-day access for passengers with same-day departures. For 2026 travelers, always check the "Lounge Information" in your app, as some smaller lounges at hubs like London Heathrow or Changi may allow a "pre-booked" 4-hour slot for an extra fee.