A layover at SFO.

Yes, if you're arriving from another country. Every international arrival at SFO clears passport control and customs, collects and rechecks checked bags, and goes back through TSA security before a connecting flight, even a domestic one. The exception is a flight that was precleared before departure, such as from Canada, Ireland or Abu Dhabi. Domestic-to-domestic connections stay airside.

LYVR shows live security wait times for each checkpoint, grouped by terminal, refreshed every couple of minutes.

LYVR shows the average customs wait for the current hour over the latest week, for US citizens and visitors, from US Customs and Border Protection's own data.

LYVR lists 18 lounges at SFO, 6 of them on Priority Pass. Which ones you can get into depends on your ticket, airline status, credit card or a lounge membership. Each lounge on this page lists what gets you in, and LYVR checks it against your own profile.

Amex Platinum Card: The Centurion Lounge, American Express - The Centurion Lounge; Amex Business Platinum Card: The Centurion Lounge, American Express - The Centurion Lounge; Amex Centurion Card: The Centurion Lounge, American Express - The Centurion Lounge; Amex Delta SkyMiles Reserve: The Centurion Lounge, American Express - The Centurion Lounge. Card benefits change, so check your card's terms before you go.

Yes, at 12 lounges: Alaska Airlines Lounge (Alaska Airlines Atmos Gold and up (long-haul international flights), oneworld Sapphire (international flights)); Alaska Lounge - Additional Fee Applies (Alaska Airlines Atmos Gold and up (long-haul international flights), oneworld Sapphire (international flights)); American Airlines Admirals Club (American Airlines Platinum and up (international flights), oneworld Sapphire (long-haul international flights)); Air Canada Maple Leaf Lounge (Air Canada Aeroplan 50K and up, Star Alliance Gold); Delta Sky Club (SkyTeam Elite Plus); United Club (United Airlines Premier Gold and up (international flights), Star Alliance Gold). Status entry needs a same-day departing flight on that airline or its alliance, and some tiers only count on international flights.

It depends on your terminals, whether you re-clear security or customs, and how far the gates are apart. LYVR adds up deplaning, every walk on the indoor map, any checkpoints your connection passes and the boarding door time, then shows exactly how much time you have to spare.

For a domestic connection on one ticket, usually yes. Arriving at SFO from another country, no: you clear passport control and customs, collect and recheck checked bags and go back through TSA security, so plan on 2.5 to 3 hours, unless your flight was precleared before departure. If a delay makes you miss a connection on one ticket, the airline rebooks you. LYVR works out your exact time to spare for your own two gates.

With an hour or two, eat near your gate and walk the terminal. With more, SFO's 18 lounges (6 on Priority Pass) have quiet seats, food and often showers. LYVR's Explore tab lists every restaurant, bar and shop near your gate with the walk time, so you only see what fits in your layover.

Yes, if you have time. Arriving from abroad, you've already cleared US immigration and customs at SFO, so leaving only adds the trip into San Francisco and back and TSA security on the return. As a rule of thumb, it's worth it with about 4 hours on a domestic layover and 6 on an international one. LYVR checks the ride each way and how much time you'd really have in San Francisco.