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)
It depends on the desired timestamp format.
If your format is supposed to look like 2020-07-12 07:52:01 for example, then you could use (assuming that you run your command from some kind of Linux/Unix):
hydra -l admin -P passwords.txt -V 192.168.0.1 http-post-form "/goform/formLogin:login_n=^USER^&login_pass=^PASS64^&curTime=$(date '+%Y-%m-%d+%H:...