Working hours never come down
If you look back at historical predictions of the future, there is invariably one about how in the future, with improved technology, productivity will improve, and the 40 hour work week will be thing of the past. Some predict a ten hour work week, others predict a five hour work week.
Productivity has improved, and in many disciplines workers do produce as much in ten, or even five hours as previous generations did in forty. But the work week doesn't go down, it just means that more is produced.
I knew a family with four generations of architects. The grandfather used to talk about how, even with slide rules and good drafting tables, it took days to do some of the more complex calculations, and a day or two to make the drawings compliant on a drafting table. Today, his grandson has spreadsheets with tens of thousands of numbers, and he can enter a modified value, and have all of the calculations - hundreds of them, if not thousands - done automatically within seconds. And the system will produce graphs showing the impact of the changes in all those calculations just as quickly.
And CAD systems have the same productivity increase compared to drafting table layouts, if not more.
As the grandfather says, his grandson can do with a keypress what took his office of three people more than a week to do back in the 1950s. And his father told him how much more efficient the architectural tools of the 1950s were compared to that were available in the 1920s.
The grandson can do more in ten hours, and in many cases in ten minutes, than his grandfather did in forty hours. But while shows like the Jetsons postulated that meant that the work day would be two hours long, he still works forty hour weeks, he just produces four (or forty, or four hundred) times as much as his grandfather did.
So, yeah, AI use isn't likely to cut down on working hours, it will just move the bar of productivity expectations.