Welllll the 40 hr work week is based off our 24 hour days and some planets have much longer than 24 hours in their day. So realistically some planets could have 60 hr work weeks. Plus we have no idea the governmental structure and ideology of other worlds and if they even allow you to stop working at all/you're worked to death or if they have such an advanced society that you don't even really have to work much at all.
Basically, this is kinda dumb.
Unions are absolutely why we have 40 hour work weeks I wasn't saying otherwise. Just that because of how our day works 8 hours of work was what people fought for. If we had days that were 48 hours things could be different and people could have fought for 10 hours days. Of course this is all hypothetical and we have no idea what people actually would have fought for.
The point isn't about how our work week works though, it's about how dumb it is to assume that other planets wouldn't have possibly longer work weeks.