As already stated, 2000 http client threads. 2000 browser threads would be quite an intensive operation to say the least... You would need a very powerful vps with lots of RAM, but even then I'm not sure BAS would handle it without crashing.
My script need to change the threads number dynamically, e.g.: 9:00-10:00 i need 30 threads,10:00-11:00 40 threads ...
What should I do?
Dynamically increase the number of threads can not. Specify at once the maximum number of threads, and let the excess threads sleep. Or use the action "Call function in several threads".