The Rajya Sabha on Tuesday made a record of sorts as it took up all the Zero Hour issues and special mentions listed in the agenda for that period, Chairman M. Venkaiah Naidu said. The first hour of every sitting of Parliament is generally reserved for the asking and answering of questions. Zero Hour is the immediately following the Question Hour has come to be known as "Zero Hour".

It starts at around 12 noon (hence the name) and members can, with prior notice to the Speaker, raise issues of importance during this time.  Typically, discussions on important Bills, the Budget, and other issues of national importance take place from 2pm onwards, according to prsindia.org.

It was during the 1960s when several issues of national and international importance used to be raised by members of Parliament immediately after Question Hour. On one such occasion, a member raised an issue pertaining to policy announcements made by the ministers outside Parliament when Parliament was in session. This act triggered an idea among other members who called for another provision for discussing important matters in the House.

As the 9th Lok Sabha Speaker, Rabi Ray introduced certain changes in the proceedings of the House to create more opportunities for the members to raise matters of urgent public importance. He proposed a mechanism to regulate the proceedings during the ‘Zero Hour’, raise matters in a more orderly manner and optimize the time of the House. 

Why is it called Zero Hour? While dictionary defines ‘Zero Hour’ as the “the critical moment” or “the moment of decision”, in parliamentary parlance, it is referred as the time gap between the end of Question Hour and the beginning of the regular business. Zero Hour doesn’t find a mention in the Rules of Procedure and hence it’s considered an informal procedure for the members of Parliament to raise matters of serious importance.

The other rationale behind naming it so can be traced to the fact that it starts at 12 noon. Members wishing to raise matters during the “Zero Hour” need to give notice to the Speaker prior to the start of the daily session. The notice should clearly state the subjects they want to raise. The Speaker is the final authority who can either reject or accept such request, according to http://www.elections.in.