This is obviously suspicious, considering most of the mails require at least a few minutes of reading + time to write the mail.
I guess adding a delay would improve the bot's credibility by a lot!
And effectiveness in stealing spammers' time. If the bot immediately auto-responds to each subsequent (presumably human-initiated at this point) email, then the spammer may more easily follow the thread.
On the other hand, if the bot waits 30-90 minutes, the spammer likely has gone on to other things. There's an additional (albeit minor) cognitive load here if they want to engage with a potential sucker.
With it, you just schedule asynchronous tasks in the future ... you don't have to manage the event queue.
I encourage you to file an issue at their source repo: https://gitlab.com/stavros/Spamnesty/issues