There could be many reasons why a domain could be available only after a few days. First of all, a .wf (Wallis and Futuna Islands) domain was only delegated to AFNIC a short while back, I think it was on the 6th of December 2011. Secondly, by registering with onlydomains and not with the TLD maintainer, it could take a day or two before onlydomains announces to the TLD maintainer the request (and approval) for the new domain. Thirdly, any TLD maintainer has typically 1 day or so of domain propagation delay (they have distributed databases that hold the domain names and registrered information, and those databases need to be in sync). You can call onlydomains to speed things up.