6 Hour Layover at Heathrow

Your bags will be checked through. I have been on longer layovers at Heathrow many times. They have lots of restaurants and shops to check out and free wifi. I've never left the airport. I've looked into it, but because of the time needed to wait in line to get out through arrivals and get anywhere would take so long, that it would be just enough time to turn around and head back to the airport. There are so many people everywhere, and while I find the airport to be very organized and moderately efficient, things are crowded and take awhile.
I wouldn't ask your friends to slog through traffic for such a short visit if I were you.

I agree with Nordheim. LHR is one of the most complex and busiest airports in the world. While you want to see your buds it wouldn't be a free-ranging, stress-free visit and you would be under significant time pressure, even with a 6-hour window. Transit times between connections there have always taken longer than I anticipated. Use any free time to window shop the abundant retailers conveniently placed in your travel path; People watching is also spectacular at LHR because it is literally a crossroads of humanity! If your air reservations aren't made yet, look into an overnight stay in London, visit, and continue to Munich the next day. Good luck!

There would be about 2.5 hours available, maybe more depending on the immigration queue. Luggage is checked through so the only other thing to negotiate is security - which you would have to do in any case.

I guess there is time for lunch in there, although you don't actually say when you are arriving or just as importantly what terminal you are flying through for any more detailed suggestions.

Pick ups have in general got more complicated because security but they could be waiting in a car park etc.

Wouldn't do it without being able to contact them if the window closes through delays.

If you are flying in and out of Terminal 5, why not meet your relatives at the Sofitel hotel for lunch. The hotel has a walkway from terminal 5 at the non-secure area. That would allow you a pleasant, relaxed meal with plenty of time to get back and thru security for your flight.

Thank you so much for all the input. We are arriving on Thursday at 10AM and leaving same day at 4:30PM. We are arriving to Terminal 5 and leaving Terminal 1. I guess we will suggest them to meet us at the Sofitel, thank you for that suggestion and the rest of the time we'll just walk around and people watch, which I love to do anyway...LOL

You won't be going from Terminal 1 as that closed down some time ago.

Interesting...our reservation says terminal 1, but I am sure we find out when we arrive. Thanks for letting me know to be alert on the change.

I wouldn't wait until then ... If you are staying on BA it will be Terminal 5, Lufthansa Terminal 2.