Not a clue yet. The window is the three weeks between 23rd june and 13th july (i.e. whent he pianos are there) but i hear there will be performances on them and stuff so I want to avoid that. Also, I might have to do it on a day when the least people are likly to be out and about playing the pianos (a monday?) which would mean taking a day off work for it. MIght have to start at 4 in the morning and do the most likely to be busy ones first. Also, I can't read music (though I can play the piano reasonably well) so I think perhaps 30 memorised peices worked out by ear is a little ambitious. Perhaps just playing the pianos will do. All of them in one day. It'll be odd to be able to say, as an old man one day, "I once played 30 different pianos in one day, all spread out across london".