The time of the exam depends on which country you are going to. If you come to the United States, you should at least take the TOEFL, because you can't apply for a good school only with IELTS scores. It is best to take the SAT (SAT 1 and SAT2 in the top 50 schools). These exams are held many times every year, so as long as you are ready to take the exam, you can take the exam next time if you don't do well.
I also took the SAT class after the college entrance examination last year, but if you come to the United States, you should first find an intermediary to prepare materials (most schools also need your high school scores and college entrance examination scores), and then apply after you have prepared all the materials and added your scores. The United States should sign in person (but if you get good grades, it won't be a big problem ~). Finally, just wait for this visa. I waited three months to sign it.
It's also good to speak Singaporean upstairs, but one thing is that there are too many people in China who basically speak Chinese, and their English will not be greatly improved. And public schools can't apply, and they have to work there for three years. If it is private, China does not recognize diplomas. One of my classmates is studying in Singapore, and she plans to come to the United States for postgraduate study in the future. She said that she is under great pressure now because her English is still poor ... but Mandarin.
If you really want to study hard, just come to America. At least I haven't regretted making this decision so far. America is really a good choice. I study accounting and finance, so I think I can learn something here.
I hope you can realize your dream of studying abroad as soon as possible ~ Come on!