Hydra http-post-form based on length of the response

I'm not sure if this is possible to do with Hydra, but I would recommend using ffuf for this.

You can do an HTTP-POST form bruteforce based on length like this:

ffuf -w /path/to/wordlist.txt -X POST -d "username=admin&password=FUZZ" -u https://target/login.php -fl 480

-fl: tells it to filter out the length you don't want (failed attempt) FUZZ: is where it will replace words from the wordlist in the request

Although in this approach the username would be static. A little bash scripting hack would solve that.