Usually the earliest closings are around the first of October. Most top schools have October or early November first round deadlines. You should have no trouble meeting those if you get the GMAT score you want on August 30th.
There are advantages to both first and second rounds at most schools. When assessing the first round, the admissions department has the most spaces available, so they are free to take most of the applicants they want. However, they may be reluctant to "over-accept" from the first round until they see what the second round applicant pool looks like. Also, some observers feel that the first-round applicants tend to be those who have planned well in advance and have their best GMAT scores and references together early. This can be the toughest competition.
Second round still has plenty of spaces open. The committee may feel free to push the acceptance list now that they have a better picture of the total pool. This may also be the point where they begin to worry about yield. Admissions committees are very concerned about "under-accepting" and being left with empty seats (and empty pockets) if the yield doesn't hold up. You are also likely to be measured against people who have had made their decision late or who have had to take the GMAT a couple of times to get their score in line.
Third round is always risky. Sometimes yields are disappointing and the school needs to accept more to ensure the class size, but more often they are looking at a nearly-full class. There are always a few slots, otherwise there wouldn't be a third round, but those slots are generally reserved for exceptional applicants.
Overall, these pros and cons tend to balance out. The best time for YOU to apply is when your GMAT, references and, above all, essays are in the best possible shape. I have counseled applicants to wait for third round and seen them accepted into top ten schools.
For those schools with rolling admissions, the earlier the better. You will not only have a better shot before the slots fill up, but you will have the advantage of knowing where you stand quickly.
Timing is crucial. Preparing your applications always takes longer than expected. Give your recommenders at least a full month to prepare their responses. Unless you are an exceptionally fast and talented writer and have lots of time on your hands for drafts and revisions, two to three months minimum is needed to get your essays in shape. The GMAT score can usually be self-reported, so that is available as soon as you complete the test. That means you should be starting with your application soon if you plan to make October deadlines.
I-20 and visa timings are unpredictable. You should always allow for as much time as possible. Many schools have different application deadlines for international students for that very reason. They may also have tighter requirements for proof of ability to pay for international than for domestic students so you need to be prepared to meet those as well. Check out your target schools and talk to your embassy to find out what your timing is likely to be.
One last point on timing. Check out the response dates and commitment dates on your target schools. I have seen applicants get into their third and fourth choice schools and need to make a deposit to hold those seats long before getting a response from their first and second choices. That can be a difficult and expensive decision.
Tani Wolff
