Building a nuclear weapon that can be carried by Iraq's missiles is relatively difficult, because miniaturizing nuclear weapons requires much more complex designs. It took the US and the USSR quite a few test explosions to achieve such a warhead.

Building a bulky nuclear weapon that fits in, say, a shipping container, is not hard if sufficient highly enriched uranium is available. That's Hiroshima level nuclear technology, the gun-type bomb.[1]

This is the difference between the "years away" and the "weeks away" estimates. Depends on whether the the delivery method is an ICBM or a shipping container.

[1] https://en.wikipedia.org/wiki/Gun-type_fission_weapon