We often hire people with jobs. At most, it's three work days needed. If that's a problem, we can do the proctored skills test on a Saturday and we can cut the on-site down to 1 day. That's then one business day needed.
Most devs with existing jobs have good jobs with decent vacation/PTO policies. So they have days to invest if they want to.
They don't hire people who have jobs because no one would/could do this.