Davkett, thanks, that was a silly mistake("came over")!
Thank you all, it's clear to me about structures with a hyphen.
As for the other variant, possessive (or genitive?) is probably a wrong term. I came across these examples - ten minutes' break, an hour's drive etc. in A.J.Thomson's,A.V.Martinet's Practical English Grammar, which was first published in the 60's, so I thought they might be a bit outdated. I also saw similar structures before in some Russian English Coursebooks. So is this variant not used at all nowadays?