Official transit threshold
ICA still uses a seven-hour transit rule
ICA's current Visa Information Booklet states that passengers transiting through Papua New Guinea for less than seven hours do not require a visa. A transit waiting time of more than seven hours requires a visa. ICA recommends applying online for a visitor visa if the wait exceeds seven hours.
That rule is the starting point, not the only operational check. Airlines also need to know whether your baggage is checked through, whether you already hold the onward boarding pass, and whether your connection can be handled without entering Papua New Guinea.