Dear Juli Rajkhowa,
The term Zero hour in reference Indian Parliament means the time immediately following the question hour in both the houses of Parliament i.e Loksabha, Rajyasabha.
This session continues for one hour from 12.00 Noon till the house rose for lunch. Since this session starts at 12.00 Noon it is called as Zero hour.
During the Zero hour the members are permitted to take up the issues of National importance and there is no specific rule in the Parliament regarding type of matters to be raised during the zero hour.