The Timestream database seems to still be in Preview, based on that I am assuming it will not be a subject on the test. Is that accurate?
To be considered as in scope for the exam, a service must be GA in US-EAST-1 or EU-WEST-1 for at least 6 months. So, preview products will not be on the exam as a scored question. Now, once it goes GA, you might see questions on the exam, but those are just test questions that AWS is trying out and they won’t be scored.