Does one really have a short time? Has anyone been asked (when they acquired) or had to show a dated receipt? I offered up a dated receipt once, and it was just shoved back with "Don't need it, keep it."
HPD enforces jaywalking far more than they do "the 5 day law". Seriously, has anyone been asked when they acquired the weapon being registered? I have been asked "Where did you get the firearm?" But never have I been asked "when", and I haven't ever hear anyone else asked too, in all the few times I have sat there waiting for something.
In fact, at this point, there likely can be made a case for doing away with the whole 5 day thing if it can be shown that it was never enforced, ever. Why have a regulation if the ones supposed to enforce it don't/won't?
Maybe the suppressor ban can get bundled in and removed too. 
The time limits are not arbitrary rules. You must register all firearms within 5 days of purchase. You must also register all out-of-state firearms brought into the state within 3 days.
Sure, you can take the firearm into HPD to register after that time elapses. Chances are, a few days won't cause problems.
What are the risks?
(1) If you don't register a handgun inside the original 10-day permit window, they can require you do the entire handgun
permit to acquire again, including another 2-week wait.
(2) If you are in a traffic stop, accident, home burglary or any other situation that warrants police involvement, and the weapon is discovered, you can be charged with possession of an unregistered firearm.
§134-17 Penalties. (a) If any person gives false information or offers false evidence of the person's identity in complying with any of the requirements of this part, that person shall be guilty of a misdemeanor, provided, however that if any person intentionally gives false information or offers false evidence concerning their psychiatric or criminal history in complying with any of the requirements of this part, that person shall be guilty of a class C felony.
(b) Any person who violates section 134-3(a) shall be guilty of a petty misdemeanor.
(c) Any person who violates section 134-2, 134-4, 134-10, 134-15, or 134-16(a) shall be guilty of a misdemeanor. Any person who violates section 134-3(b) shall be guilty of a petty misdemeanor and the firearm shall be confiscated as contraband and disposed of, if the firearm is not registered within five days of the person receiving notice of the violation. [L 1988, c 275, pt of §2; am L 1994, c 204, §9]
§134-2 Permits to acquire. (a) No person shall acquire the ownership of a firearm, whether usable or unusable, serviceable or unserviceable, modern or antique, registered under prior law or by a prior owner or unregistered, either by purchase, gift, inheritance, bequest, or in any other manner, whether procured in the State or imported by mail, express, freight, or otherwise, until the person has first procured from the chief of police of the county of the person's place of business or, if there is no place of business, the person's residence or, if there is neither place of business nor residence, the person's place of sojourn, a permit to acquire the ownership of a firearm as prescribed in this section.
134-3(b) Every person who acquires a firearm pursuant to section 134-2 shall register the firearm in the manner prescribed by this section within five days of acquisition.
Youse pays yer money, and youse takes yer chances!
