If deorbiting in years is sufficient, the difference in 1 minute vs 4 years is NOT relevant -> to a satellite builder worried about the law.
If everything deorbits within 5 years, the only way for more things to accumulate is to launch things faster. But that's a separate discussion. If everything launched today is deorbited within 5 years, then in 5 years, all satellites will be new satellites launched after today. If everything launched today is deorbited within 5 months, then in 5 years, all satellites will be new satellites launched after today. Deorbit speed under a threshold has no bearing on accumulation beyond that threshold.
If SpaceX launches a trillion Starlink satellites, and they all deorbit within a year, then yes. it's going to be a very crowded year, and we'll have to drastically rethink how much stuff we have in LEO, but at the same time SpaceX would not be in violation of the 5 year deorbit window, so the issue is about how much stuff we're sending up, and not how fast it de-orbits.
"Amount of junk below 450km, total" and "Amount of junk below 450km, that hasn't deorbited after 5 years" are very different things. You're making points about total, while the original point was about deorbit speed.
One time is 10^12 times longer, but the difference does not matter to me. My emails are still sent and received faster than I can possibly perceived.
If something was going to deorbit within 1 minute, or was going to deorbit within 4 years, 6 months... It doesn't matter to the creator, because they don't have to change their design at all to meet the rules.
If something was going to deorbit within 8 years (because they previously had a 25 year allowed limit), they now have to rework the design.
There's plenty of room for debate about if 5 years is adequate, but as it stands, _most_ things (under 500km) will naturally deorbit within the legal time frame anyway even without special consideration.