DNS changes to the WHOIS of a domain are carried out after authorisation in real time. The activation of the new entries can take between 4 and 6 hours for a .AT domain, and for generic TLDs, such as .com/.net/.org/.info/.biz, the changes will most likely take 24 hours before they are completed. This delay is due to the different reload times of the root servers used by the domain name providers (.com/.net etc).
In contrast to that, zone changes are already active in name servers which have already been registered. However, it takes between 4 and 12 hours until changes will come into effect with all providers.