There's a back-and-forth on that opinion piece, here [1] and here [2].

[1] http://iranmatters.belfercenter.org/blog/iran-op-eds-fatal-f...

[2] http://iranmatters.belfercenter.org/blog/misleading-spin-cen...

On the key point of low enriched Uranium, here's the text from the agreement:

> During the 15 year period, and as Iran gradually moves to meet international qualification standards for nuclear fuel produced in Iran, it will keep its uranium stockpile under 300 kg of up to 3.67% enriched uranium hexafluoride (UF6) or the equivalent in other chemical forms. The excess quantities are to be sold based on international prices and delivered to the international buyer in return for natural uranium delivered to Iran, or are to be down-blended to natural uranium level. Enriched uranium in fabricated fuel assemblies from Russia or other sources for use in Iran's nuclear reactors will not be counted against the above stated 300 kg UF6 stockpile, if the criteria set out in Annex I are met with regard to other sources. The Joint Commission will support assistance to Iran, including through IAEA technical cooperation as appropriate, in meeting international qualification standards for nuclear fuel produced in Iran. All remaining uranium oxide enriched to between 5% and 20% will be fabricated into fuel for the Tehran Research Reactor (TRR). Any additional fuel needed for the TRR will be made available to Iran at international market prices.

That would seem to add 2 months to the breakout time. i.e. It would be 5 to 6 months based on Kuperman's reckoning (as opposed to Obama's claimed 12 months). Whether they can divert or reconstitute some of the 20% material during or after fuel conversion is unclear. Some scenarios are discussed here:

http://www.isisnucleariran.org/assets/pdf/LEU_20_percent_upd...