Thanks for the hint.
I looked into DNS, and I failed to find any information or I couldn’t solve the problem.
I had the localhost in my resolv.conf file and my firewall (Untangle). I removed the firewall from my DNS entry, leaving only the localhost as a DNS server, and I still have that delay, for any type of call… shouldn’t it solve at least the internal call ? (I may be wrong on this assumption). I know my change works because now the Asterisk can’t do opencnam query.
Is there a way to deactivate any reverse DNS made from Asterisk ? It would help to narrow down the exact problem I have…