O'ahu vehicle registration - how long does it take?

Aloha from Kaua'i. Bought a used vehicle from a dealer on O'ahu, had it shipped here. The dealer is telling us that it takes 60-90 days to get a vehicle registration processed on O'ahu? Does that sound right? They insisted that it has to be done there, because I offerred to do it here myself, and it's same day service. Anyone know? Mahalo, in advance...