First up, congratulations to all those who have received interview invites!!
Alright, so I have read the entire thread and have seen people trying to relate the time when applications were submitted with the time the interview invites were rolled out. So just thought I would chime in with whatever knowledge I have gained so far, which is to a very large extent through a discussion with one of the Associate Directors of Admission at an Information Session...
Ross follows a very unique approach to admissions with regards to the Admissions Committee itself. Unlike other schools, Ross appoints Regional Managers - people who are responsible for selecting the best of the candidates from an entire region. These people, through years of experience of screening applicants from a particular region, develop the expertise in understanding regional attributes such as average GMATs, GPA scales, good undergrad institutes etc. The following regions have dedicated regional managers - US, South America, India, Europe & Africa, South east Asia minus India. I am sorry but I don't know in which regions do countries such as Mexico that don't fit any of these regions fall under. Also, there might be more regions but I may not have been told about all of them by the AD.
So the lifecycle of an application goes something like this -
1. Once an application is submitted, it is submitted to the first reviewer. The distribution of applications to first-level reviewers is completely random. The demographics of the applicant, GMAT or other credentials and even the date of submission of the application are completely irrelevant. Since the randomization is inherent to the first step, it just goes to show that the rest of the review process will also follow a random path. Hence, people who have not yet received invites need not be disheartened.
2. Now, the first reviewer filters out only a very very few applications - applications that truly don't deserve to move forward. He/she also puts in his/her commentary on that application.
3. The application moves to the second reviewer who again tries to filter out some applications. Again not very many are eliminated at this stage since they are trying to find all the potential good attributes in all applications.
Note that the second reviewer could be a Regional Manager for some other Region. For example the file could be for a Chinese applicant but is being reviewed by the RM for Europe & Africa.
4. Finally, the file goes to the RM for that region. Now the RM will receive files from all 2nd level reviewers for all applicants belonging to his/her region. Having a comprehensive view of the entire applicant pool for that round, the RM will compact the list for that region. This compacted list is more or less the list of applicants that are invited to interview. However, interview invites are not sent out once the entire list is finalized. They can be sent out depending on the certainty the RM feels for each of the candidates. Hence you might have people in the same region receiving invites across dates.
5. Earlier, invites were sent out as soon as the RM felt certain that an applicant had to be interviewed. However this led to a lot of stress on the interview team. Ever since, they have decided to release interview invites in batches so it is easier for the interview team to schedule interviews in an orderly manner. Also, note that the interviews are blind i.e. the interviewer will have access only to your resume; the interviewer will not have read your entire application.
6. Once the interviews are over, the RM filters out more people and sends the final list to the Dean / Director (don't know the exact position) of Admissions. He/She has the final authority on all admits & declines. Looking at the overall global applicant pool, the D/D will take a final call on each applicant in each of the RMs lists. This is an especially critical step since only the D/D really has the visibility into the overall pool of applicants and this helps him/her in crafting a class with the diversity the school deems necessary.
Hope this helps!! Again, this is what I understood from my interaction with an Associate Director of Admissions at an Information Session. I will be happy if any current student / alum who has firsthand insight into the admissions process can add anything or correct anything in whatever I've written above!