Based on my experience when I was studying (Non-MBA course) at NUS many years ago
a- If you're working part time, you can only work 16 hours a week. This part time work can be related to any field. This can include working at McDonalds
b- Industrial attachment is like internship where a student is working full time, 40 hours a week for whole summer or one/two semesters. Normally, such industrial attachment is part of your degree requirements considering you are working full time.
If you are doing internship as part of your MBA requirements or something arranged by INSEAD, you don't need to worry. You can work 40 hours a week during that internship. But if you're planning to do something on your own, you can only work 16 hours a week.
I was wondering. Do you think you'll be able to get time to work part time while studying full time for MBA