Depends on factors such as how soon you respond to NVC's requests, when a visa is available, etc.
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The scheduling is not done solely by the NVC. It also depends on the availability of calendar "slots" available at the US Consulate at which the case is pending. I would say that a minimum of 1-2 months may pass before you receive notification.
This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice. A consultation with an experienced attorney is always the best way to go.
It will greatly depend on how busy the U.S. consulate in question is and the available time slots for interviews. I would dare say at least 2 months, if not more.