A.WHOIS databases are specific to each registrar. If you registered the name properly, it will show in our WHOIS database immediately. It will show in the InterNIC central database 24-48 hours later, but might not ever display in another registrar's database. That doesn't mean someone else can register the name, the name record is still taken, but it might not show you as the owner.
Your best bet is always to look up a domain at the registrar of record. To find out who the registrar is for a name, go to http://www.internic.net/whois.html.