From a physical standpoint there are enough hours in a week to work 40 hours and pursue 40 hours of university.
Except universities aren't something like an evening school that is explicitly designed around this idea. University lectures do not follow a nice time table that allows that. Lectures start at different times depending on the day of the week. Therefore your workday will start at a different hour every day, except all your colleagues still work their 9 to 5 schedule which will make you significantly less productive than them because you don't get to meet them every day. There can be gaps between lectures but you can't just go back and forth between university and work. It takes time to travel and even if you can do it in a reasonable amount of time you will end up doing multiple context switches per day. This makes working significantly more than 20 hours per week extremely hard.
Except universities aren't something like an evening school that is explicitly designed around this idea. University lectures do not follow a nice time table that allows that. Lectures start at different times depending on the day of the week. Therefore your workday will start at a different hour every day, except all your colleagues still work their 9 to 5 schedule which will make you significantly less productive than them because you don't get to meet them every day. There can be gaps between lectures but you can't just go back and forth between university and work. It takes time to travel and even if you can do it in a reasonable amount of time you will end up doing multiple context switches per day. This makes working significantly more than 20 hours per week extremely hard.