Most bots select the GMT-12 timezone, you can block their registrations with this...
https://vborg.vbsupport.ru/showthread.php?t=141554
It is working with 3.7.3 for me, Ive had 2 bots in 1 1/2 years
also, and this is just a suggestion, Im not sure how right I am about this
turn off email verification, the bot software waits for the verification email, verifies, then posts spam, if the email never comes they may never post, even if they manage to register.