support(at)zohoaccounts(dot)com how long do they take to respond

support(at)zohoaccounts(dot)com how long do they take to respond

I contacted support(at)zohoaccounts(dot)com today at 16:03 (GMT+1) because I am unable to add a new domain to my zoho account and the error message said to contact this email address.
Three hours later and I have received no response whatsoever, not even an automated acknowledgement of receipt. What is a reasonable length of time to wait for a response from a professional, paid for, service? I would say 3 hours is too long. I need to get email up and running for this new domain so when my plea for help via email was ignored I came on this forum only to discover that they won't discuss this issue on a public forum, for security reasons. So, email support is the only my only option, and they're not listening.
Can anyone tell me what waiting time I should expect. I don't even know if my email has reached it's destination, surely an initial automatic response can't be too much to hope for.