Yeah a 13 day fortnight is really a really big ask especially when the days are long and I wouldn't wish that on anyone. We all need time off.
I guess we're all different but I don't see why it's important that the days you have off are saturady and sunday.
Obviously for Jewish workers it's important that they don't work on the sabbath and there are Christians who aren't comfortable working on Sundays and Muslims who like to have Fridays off so they can go to Friday prayer but the great thing about a multi-cultural work force working a week of 7 days is that all these wishes can be accommodated.

ETA - the thing that bugs me is when companies want to remove penalty rates for working on public holidays, at night etc.