I think they mean that it's 4-6 weeks until they hit zero, accounting both for stored products and the current rate of production/imports.

Usually when something like this is reported, it is because of some other milestone.

Like, they have 6 weeks, on hand, in tanks already delivered.

But, all of the ships in-bound are now done.

After the war started, there was a record number of ships, already filled, already in-transit. But now they have all reached their destinations. So there is no more incoming.

Yeah, but what's the burn rate?

If it's going down at 1 day per week then it's not so bad. If it's closer to 0.75 days per day, that's much more serious.