I've worked in the graphic design industry for over 10 years and the amount of time you spent on projects/work really depends. Here's my experience from:
Printing company: Worked during college, hours are generally flexible bc they don't really need you to do much work.
Design agency: Worked during college, hours are also flexible, but the project have extremely short deadlines and you have to work in a fast pace.
Start-up: My first day, I worked 12 hours. No joke. But we were launch our site, so it was expected. Hours in a startup are more crazy than other places, only because they have a fast turnaround.
Corporate (LinkedIn): They are very family-oriented so people usually work the generic 9-5, but when there are projects due, you are expect to finish on time. I've been up until 2am, sometimes weekends working.
Honestly, I think as long as you love what you do, the time isn't the issue. I love designing and creating experiences for our members, so working doesn't seem like working.
Hope that helps.
Dream big, Vivian