"I need eight hours of sleep every night."

Translation: Jag behöver åtta timmars sömn varje natt.

[breravin]

'timmars' - I haven't seen that before. How do you know when to use 'timmars' instead of 'timmar' for hours?

[Beanybadger]

It is perfectly natural in UK English to say he got eight hours' sleep, or it is in three weeks' time. I think it is not just a Swedish construction.

[steverandall7]

Still, we've never seen this construction before and I don't think it has been explained.

[SKlassen1]

of course this example is ambiguous at best because in english we also make plurals by sticking an s on the end. It does not really make sense to speak of the hours owning the sleep or the weeks owning the time. The real question is whether in swedish it is a possessive form or a plural.