As you have asked about the IIT JEE mains important dates, check below for the information
JEE Main 2016 Important Events

Events Dates

JEE Main 2016 Application Date 1 December to 31 December, 2015
Last date for submission of applications 31 December, 2015
JEE Main 2016 Admit Card online 2nd week of March, 2016 onwards
JEE Main 2016 Pen and Paper based
(Offline) Exam Date 3 April, 2016

JEE Main 2016 Online Exam Date 9 April, 2016 & 10 April, 2016
JEE Main 2016 Answer Key & OMR display 18 April to 22 April, 2016
Result of JEE Main 2016 27 April, 2016
Declaration of Top 1.5Lakh candidates
eligible for Advanced JEE 27 April, 2016

Declaration of All India Rank On or before 30 June, 2016

JEE Score Card to download on official website After declaration of AIR