It depends on the details of the work sample test.

If I ask you to write me a python function to convert OSGB easting/northing into WGS84 longitude/latitude the task has a very clearly defined scope. If you knock it out in a quarter of the allotted 4 hours, you've saved time. You can't use the remaining time to go further and demonstrate your mastery.

On the other hand if I ask you to write me a website for organising photos, there's no such thing as 'done' - no matter how good you are, after 4 hours you'll still be able to think of ways to make it faster, more beautiful, more featureful, more scalable, cheaper to operate, etc

Obviously, as a hiring manager I'll notice if you've spent 40 hours on the 4 hour task - but if you've spent 6 hours maybe I just think you're a fast worker with relevant experience and sharp tools. And my sense of how far you can get is calibrated by other prospective hires; if lots of people are spending 6 hours and claiming to have spent 4, my expectations will naturally be high.