Lectures at most unis will be scheduled between 9 and 5, but what times and days your lectures at will change year on year, term on term. You may have a term with a 9am lecture every day, and nothing for the rest of the day mostly. You might have one where you have 6 consecutive hours of lectures on a Friday but only one or two odd hours the rest of the week. You might end up with all your lectures starting at 11am each day and finishing by 2!
That said generally the students who get consistently good results tend to approach it as a 9 to 5 job, consistently going to campus every day in the morning, working through the day while attending timetabled hours, then "clocking off" at the end of the day. This also likely helps avoid burnout and maintain a good balance of uni work and personal life as then you know you've done work throughout the day so don't need to feel pressured to spend weekends/evenings working on things last minute so much!
Bear in mind also in principle full time uni study is based on the expectation you're going to spend a number of hours on your studies equivalent to full time work, across the the teaching terms. Of course in practice usually students do and can spend less than that much in term time by making up time during the breaks working on assignments or revision (and often due to when things are set/deadlines are this is necessary).
So while you don't necessarily need to work a full 9 to 5 each day i would suggest aiming to start at a set time each morning around 9ish to get into a good habit - then you can finish whenever you are comfortable that you've done what work you need to do that day.