The informal period in a House of Parliament, immediately after the Question Hour, when members raise matters of urgent public importance without prior notice.
The contrast between the formal, rule-bound Question Hour and the informal Zero Hour is a frequently tested parliamentary-device distinction.
Zero Hour is not in the rule book and has no fixed time limit, unlike the concept question hour which is regulated; Zero Hour follows the Question Hour, not the reverse.
Informal noon slot after Question Hour for urgent matters; an Indian innovation, not in the rules.