It's a headline in the Mail and it's about the Labour Party. So you should start from a presumption that it is spun to kingdom come. And sure enough, without even having to seek out any sources beyond paragraph 2 of the Mail's own article, we see that a crossbench peer suggests shaving 2 and a half hours off the current standard public sector working week by 2030 and, perhaps, influencing private sector employers through example/market forces. The Mail does the maths and concludes that this could be achieved by lengthening the working day and doing four instead of five. Sorry, FOUR instead of five, forgot the OUTRAGED caps lock.
Buried much further down the article is the fun fact that British workers have the third longest working week in the EU. That isn't something to be proud of and it will get worse after Brexit - one of the key goals of the hard Brexit Taliban is to get ordinary people working longer hours for the same or lower pay, makes us lean and competitive you know.