"Iran must reduce its large stockpile of low-enriched uranium to no more than 660 pounds from roughly 12 tons today — a 98 percent reduction. To do so, it will almost certainly have to ship fuel out of the country. It must also disassemble and store more than 13,000 centrifuges — it is allowed to have only 5,060 spinning — and convert the underground Fordo nuclear enrichment site to a research-and-development installation. Iran must also remove and disable the core of its heavy water reactor at Arak so that it cannot produce plutonium, another pathway to a bomb. It must also make arrangements for inspections and monitoring by the International Atomic Energy Agency and begin answering questions about suspected military-related work on nuclear weapons — although the answers may take years to resolve, if they are ever resolved."
— No one is quite sure when all of that will be done, but the European Council on Foreign Relations estimates four to six months. The Times says American experts estimate Implementation Day won't be official for six to nine months after Iran begins to dismantle its nuclear program.
— Once all of that is done, the U.S., the European Union and the United Nations would drop, or in some cases suspend, nuclear-related sanctions.
— According to the European Council on Foreign Relations, parts of the agreement begin to expire in 10 years. The clock on some of those parts are tied to Adoption Day, while others depend on the timing of Implementation Day.
Update on Oct. 16 at 11:39 a.m. ET. Adoption Day:
We've updated this post to reflect that Adoption Day could be Oct. 18 or 19. The JCPOA defines adoption day as 90 days after the U.N. signed off on the deal. That would make it Oct. 18. The State Department said Adoption Day would be "about October 18th." Iranian Deputy Foreign Minister Abbas Araqchi, however, said Adoption Day will be Oct. 19.