I got a reply from Zoho. "The usual delay in email fetching should be around 1-3 minutes. If you are consistently facing higher delay times in email fetching. Please send the respective email headers and ticket ID details to support"
To be honest, 3 minutes is too long for me. FreshDesk is a few seconds. I prefer to do support via e-mail rather than a browser portal so maybe that's why it's a big issue for me but not others.