I would say best practice now that they are doing walk-ins is to try to get there within the 5 days. The waiver of time was entirely at the discretion of the Chief of Police per the order
Sections 134-3(a) and (b), HRS, registration, mandatory, exceptions, to
the extent necessary such that the chiefs of police of the counties, in their sole
discretion, may suspend the deadline whereby a person must register a firearm
within five days after arrival in the State of the person or firearm, whichever
arrives later, and the deadline whereby a person acquiring a firearm pursuant to
section 134-2, HRS, must register the firearm within five days of acquisition.
But if they turn you away, try to get as much info from the officer (name/badge no./etc.) so you can note it when you do go back and harassed