Do bears s%&t in the woods!
Very well worth it.....
Jump off at the Colindale underground station, it's a 1/2 mil walk or so, free entry, yes FREE entry! You have the Battle of Britain Hall, with some German rareities Ju88R, He111, Me110G, Stuka, also Huri, Spit and a superb Sunderland you can walk through (plus many others) on that side you have a good resturant.
Then if you're lucky the original Grahame White WWI refurbished hangars will be open (not always, due to staff levels). Full of very early ac and WWI ac.
Then on to the main halls, with so much in, you will be amazed. From the inter-war era, through WWII (P51, P47, Mossie, Me262, Tempest, B25, B17, Lanc, Battle, Halifax, (Wellybag is being refurbished), Fw190, He162, Typhoon, Spit et al, through early jets Vampire, Meteor, mid Lightening, Vulcan, Buccaneer and late jets Harrier, Typhoon 2, helo's, flying boats...too much to mention, then the shop to get that flexible friend flexing!
And no I don't have anything to do with Hendon, but it's just such a good museum..
If not there, then the Mosquito Museum at London Colney. Not easy to get to without a car, and out of London by some way, also it's not open every day as it's manned by volunteers. Small but well worth a visit, but possibly not effective for the time you have.
Then there's into London and the Imperial War Musem, (get off at the Elephant and Castle underground stop...3/4 mile walk) a bit of everything (mainly land and air warefare), and again free. Very good, but if you're into aviation then Hendon is the place.
Duxford, again superb and on par with Hendon, is some 50 miles away in Cambridgeshire, and again time and access without a car would be a problem.
Hope this helps and enjoy whatever you do!
Cheers
Shessi