TOFL is an exam necessary which is accepted by many abroad universities.
A detailed information about the pattern of exam can surely help you to execl it.
In my opinion you should apply for TOEFL after your board exams because you will get enough time for the preparations and it actually depends on your capabilities whether you will take more time to prepare for the exam or not.
Here is the link for the exam pattern -
See, if you consider my suggestion then use your 12th Summer Vacation for your toefl. It is not that difficult exam and you can easily prepare in 20 days max.
TOEFL scores are only valid for 2 years.
Just keep in mind that If you want to start college in 2021 the you will have to submit your application in Dec 2020.