I WILL BE COMING INTO LONDON AND HAVE A 5 1/2 HOUR LAYOVER...DO I HAVE ENOUGH TIME TO TAKE THE UNDERGROUND TO THE BRITISH MUESUM AND BE BACK FOR MY FLIGHT ????...AT 17:30...WILL THE LINES BE LONG-
CUSTOMS..ETC...WHAT CAN I DO AT THE AIRPORT FOR 5 HOURS..????

Eat & shop

You certainly don't have enough time to get into London and I'd say it's touch & go whether you could take the short ride to Windsor

Please don't shout

Probably not, because your layover will be markedly shortened by the amount of time you have spend in immigration and security lines when you arrive and depart. The (incoming) immigration lines at Heathrow are terrible -- there's a good chance you could spend an hour there.

So, even if your plane lands on time, figure 60-90 minutes before you leave the aiport, and then you have to get back at least 90 minutes before your flight, plus about 30 minutes each way into the city. A little math shows that your 5 1/2-hour layover will be whittled to about a half hour.

Hi Jer. BTW Heathrow

Go to the British Airways Terrace Lounge in Terminal 1. Try a glass of wine from each bottle they have. You will be surprised how fast the 5 1/2 hours will go.