Rolling Admissions: 10 Frequently Asked Questions

“1. What is rolling admissions?
2. Do rolling admissions colleges have any deadlines?
3. When is the best time to apply to college under rolling admissions?
4. What is the latest date I can submit my college application?
5. When will I receive an admissions decision?
6. Are rolling admissions decisions binding?
7. What is the difference between early action and rolling admissions?
8. Are there disadvantages to rolling admissions?
9. How can I tell if a school has rolling admissions?
10. Which schools offer rolling admissions?” …

https://www.usnews.com/education/best-colleges/articles/2018-01-11/rolling-admissions-10-frequently-asked-questions

University of Michigan has its own way of rolling admission for RD and is not on the list. It only means the admission notice MAY come out much earlier than the final announcement deadline in April. Early application is encouraged as they start the evaluation before RD application deadline.