You're right about "girls' school", but "a ten minutes' walk" is wrong (should be "a ten-minute walk" or "ten minutes' walk").
Thanks. I myself am a non-native speaker.
[Note to self: I should re-read the relevant chapter in my English grammar when I get back home. Meanwhile, I'll look at the overview here.]
(Semantically, “ten minutes' walk” still means ‘a ten-minute walk’ rather than ‘the ten-minute walk’, but your point in reply to shminux was about syntax not semantics anyway.)
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
Of course, for "every Monday", the last one should have been dated July 22-28. *cough*