Timeline? I have not taken the GMAT yet

If you have not at all worked on any other part of the application package so far,and would now begin preparing for your GMAT scheduled for December end , you hardly have any time to apply in the Round -2. Unless you are super keen to apply in Round -3, I would suggest you to give yourself more prep time and apply in the next Fall.

Some round 2 deadlines are in January, so you can probably make it. Keep in mind you don't have to wait for the official GMAT score to apply.

It depends on your schedule. If you can work concurrently on your applications with studying for the GMAT, I'd say it's possible to get applications in for Round 2 in January. If not, I'd recommend holding off until next year.

Yes, you will have a chance to 'apply' with a slim possibility of being admitted. Since you plan to take up your GMAT, say in December, the results will be out by the end of January. That means you have lost the most fertile Round 1 of admissions and will have little time or may be no time to apply for the more competitive Round 2. This leaves you with cutthroat competition or sometimes even sterile Round 3. Therefore, it will be better if you apply for the Round 1 of the next batch. Although the institutes claim that applying in any of the three rounds does not affect your application status. However, practically, most seats are filled in Round 1 itself. Several institutes even offer scholarships and apprenticeship to be availed in this round. Round 2 aims to fill up whatever seats are left out. By Round 3, hardly any seats are left. Therefore, apply early is the ground rule for getting the college of your choice.

Thanks for everyone's advice. Looks like it might be my best bet to look into admission to the next school year.