They’re playing games with the EU, and only giving them a few hours to sweeten the pot so they won’t start their nuclear program back up.
Honestly, it probably won’t matter in the end anyway since they seem fairly determined to start their program back up.
From the BBC:
Iran says it will wait until later on Monday for European Union proposals on resolving the impasse over Tehran’s nuclear programme.
Tehran had pledged to resume converting uranium at a plant in Isfahan after a unilateral deadline expired on Sunday.
The delay to Monday evening offers the EU a few more hours of negotiations.
Iran halted all uranium conversion and enrichment in November 2004 because of international pressure, but denies charges of pursuing nuclear weapons.