how are they going to know if the info is input a week later?
C"mon, use your imagination. There are a whole host of scenarios that could play out. Here's a possible one:
Seller and buyer meet FTF in a parking lot somewhere with no (reasonable) internet access. They examine each others' LTCs (as is done today via FA-10), agree to the sale. Seller jots down the buyer's info and will fill out the stuff on the web portal when they get back home. All good, right?
Buyer has an accident on the way home, and the police search the vehicle (or "inventory the contents") prior to it being towed. The gun is turned up, and they check the database and find that it's registered to the Seller. They now have evidence of not complying with the web portal law.
Probable? Maybe, maybe not. Possible? Yes.
Under the current law, while there may be a bunch of BS to deal with, neither buyer nor seller has broken the law.