1) In a case interview, is it possible to be rejected for taking too much time to think (but you got all the answers right and had good structured thinking)?
I can’t see a scenario where the interviewer will reject you because you needed a bit of extra time.
The issue that you may have if you need a lot of time to structure is different.
If the interviewer thinks you had enough time, he/she may ask if you can present what you have. If your structure is then incomplete (because you didn’t have time to finish it), it may not be appropriate / MECE. And that could be a possible reason for a rejection.
2) If I maintain the 2-2:30 minutes time along with my accuracy, would this hurt me?
In general that's fine. Just be ready for the fact that the interviewer may ask you if you are ready and to present what you have if you take longer than what he/she expects.
In any case, if the alternative you have is a weak structure, you should take the additional time. Better to take a bit longer and have a better structure.
Hope this helps,