Project engineers may adjust their hours based on the stage of the design. Design, fabrication and assembly. Different groups may need technical expertise at different times of the day because it’s your design.
There may be travel involved and onsite support at a customers facility.
Don’t be afraid to ask questions from engineers, who work in the industry you are interested in.
I've been an engineering consultant for over 10 years and have over 20 years of experience. I travel between my consulting jobs. My income is less consistent than salary folks, but I have more freedom. It's not for everyone.
Time spent on the job will also be affected by your experience level in handling the types of tasks you are given and familiarity with your company/job. If you are new to engineering or are new to a company, extra time will be needed to learn the details of what and how things get done. Being a professional/salaried job, a typical expectation would be that you dedicate yourself to the job (whatever it takes) to complete the specific tasks of your job within the committed schedule. Finally, there is an aspect of personal drive that comes into play. Do you want to do the minimum work required, or are you eager to get ahead and maybe do more than you are asked?
In my personal experience, work has ranged between 40 - 70 hrs.