Heathrow airport customs?

In August I will be traveling through Heathrow airport for a connecting flight. We have a 6.5 hour layover. How long do customs usually take and if we do decide to leave the airport what could we have time to see. We have never been to London and would love to see something if there's time.

Added (1). I will not have luggage because it will be transferred from one plane to the next. Our plane lands at 1030 local time

If you have a UK or EU passport, it is usually quicker than other passport holders. Last year, there were long delays; not sure how it is now… There would not be much time to travel into London, and be sure to get back on time.

Queues dominate Heathrow Customs and Immigration and you need to check in for your next flight 2 hours before departure. Sadly I think you need to stay in the airport

There's no guaranteed Customs time. It depends on what planes landed a few minutes before yours how long the lines are. Fast is about 30 minutes. A longer wait can be hours.

The Airport is not close to much for tourist purposes. You will probably need to also go through a security check for next flight.
You have about 2-3 hours free time to wander the terminals. More than enough shops, art work and other stuff to keep you busy.
Where did you get the magic 6 hours and 30 minutes time.
Do you have a guaranteed arrival time? Depending on winds an hour early or late is NORMAL
Will you be first off the plane the minute it lands? Last off could be 30 minutes after you land.
Will you be able to board next flight up to last minute before departure.

A stop for the toilet, something to eat and drink a souvenir or two and your time is up.

You could take a train somewhere for a few minutes to explore and then return to Airport, Up to you to decide if 15 or 30 minutes at some place is worth the cost and travel to and from time. Allow time to get to train station purchase a ticket and the waiting time for next train.in addition to just time on the train in your planing for an adventure away from the Airport.

Of course you will have perfect weather that day and the Airport will be running normal no extra crowding no lines. IT HAPPENS just do not plan on it.

Use the connection guide to help plan your time at Heathrow

You will have to recheck your luggage or haul it around with you during your adventure.

Depending where your next flight is to is if you have a quick pass and avoid a Customs check in UK and do it at destination. If you want to leave Airport you must pass a Customs check and security check when you return.

Windsor is closer

I would reckon on at least an hour to get through immigration and Customs, though if your luggage is being transferred directly to the other flight, Customs won't have that to look at! Customs is usually quite quick at Heathrow. What they do is if you have "anything to declare", you go through the red channel and your luggage will be examined, but if you have nothing illegal or over the duty-free limit, just walk through the green channel. You MAY be stopped in the green channel if you look suspicious to the Customs officers, but of course they're not telling us what looks suspicious!

What takes the time is immigration (passport control). Most transatlantic flights west to east go overnight and the immigration queue at Heathrow at breakfast time has to be seen to be believed.

Heathrow is 14 miles out from central London so count on 2 hours to get there and back by Underground. Plus it is recommended that you check in 2 hours before your next flight. This is not going to leave much time left and personally I wouldn't risk it.

Customs won't slow you down unless you're very unlucky or carrying declarable goods. The problem is you don't have enough time.

Even with local familiarity, and assuming nothing goes wrong, it would be a dash just to reach anywhere worthwhile and make it back, never mind actually experiencing anything. From touchdown you have at least 20 minutes before disembarking, then immigration / passport control, the distance to travel back and forth between Heathrow and London, finding your way around, and check-in 2 hours before flight.

I would want a minimum 12 hour layover if I planned to visit central London between flights for any reason, other than a dire emergency, and that's with good local familiarity and masses of travel experience. Factor it into your next trip instead and we can advise how to make the most of it.

It is a British custom that if you are working dealing with people who might be on holiday, to do you job as slowly as you can and be as surly as you can be. Heathrow Immigration and security take this to a whole new level empolying only 5 star jobsworths.

You can't leave the airport if you are having a layover, you will not be immigration cleared and will have to wait in the airport.

" if we do decide to leave the airport ".
You can't leave the airport.