I knew a ChemE who graduated in 3-1/2 years while going to summer school and doing internships. She was a workaholic. I saw her literally mowing the yard while looking at index cards. It seemed like everyone in engineering knew her. She was getting scholarship awards/money even after she had graduated and left the school. I'd never seen anything like it. She could never explain anything though and admitted she could never apply it. She said she just tried to memorize everything. She ended up getting her PhD and lives in CO. Her and her brother were my best friends in college. He was in EE and ended up having a complete nervous breakdown. Was never the same person. It was because of him and my own struggles that led me to switch from EE to ME after 2 years and I graduated in a total of 6 years after internships between semesters. I worked part time in the computer science dept during school. I considered working a break from studying.It was relatively common at my school... I only took summer classes since I was trying to dual major so I took psychology & philosophy over the summer at a cheaper school to transfer (so then I could put just enough effort in so the classes transferred, the grades didn't affect my GPA, and I was working multiple jobs)
graduating in 4 years is pretty common in my experience - sample size being my classmates & coworkers tho.