I am pulling these numbers out of my a* but comparing to the situation in Twitter. People can be enthusiastic to move but if a significant portion doesn't do it in a certain window of time, they'll just drop out of it.

Let's say this portion is around 60% of Tiktok users. So something like 60-70million and window span is 10 days. They need to sustain 6-7 million new US users per day in order to make a successful transition.