It seems to be a fairly general problem.
I signed up on Tuesday, and initially, DNS worked fine, but as of Wednesday, any changes (e.g. adding subdomains) never become active in DNS.
I asked Support about this, and (after >1 day!) they manually reloaded the DNS. That helped for outstanding changes, but a subdomain added after that has still not become active in DNS.
Also, my brother signed up yesterday and has the same experience as you: all OK in whois since yesterday evening, but nothing yet in DNS.
The “sub-domains” thread in this forum seems to describe the exact same issue.
I mailed Support (again) about this, no reply yet.