Djmatte provided a good response. Many NPs do work 2 jobs to make extra money - a full time job and a part time job like home health assessments. Depending on the practice, there may be opportunities to make extra money by working evenings and/or weekends.
Some experienced NPs choose to work locum tenens ("temp") positions. They can get a very high hourly rate, but no benefits. Here in California, a primary care locums NP can make $200K per year. That can be much higher for other specialties like psych.
As far as not adhering to scheduled hours, that depends on the individual practice and also, the specialty. There are plenty of jobs where little to no OT is required or expected - SNFs, schools
, sleep medicine, etc. However, if you are working in a very busy urgent care practice, you probably will work OT. This is something you can find out up front when interviewing for a job.