In principle, you could create a custom style variant that would treat the locator (page, etc.) value as a time, specifically for the Interview type. Or I think you could also specify one type of locator as if it is 'time'-- say part or something you're unlikely to ever use like verse or Sub verbo.

However, a simpler way would just to type out the time as a suffix to the cite in whatever format you want. It wouldn't be automatically formatted, but since Zotero doesn't generally "do" anything with the pages cited you won't lose any other functionality.

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You might want to mention this as a feature request for the updated item types coming in the next release. (It's possible it's already planned.) "Interview" is a fairly general format so I can imagine it having various types of locators. But "time" in general seems useful, not just for Interview, but also for Audio Recording, Film, Podcast, TV Broadcast, Video Recording, etc.

Actually, you might look for other discussions about how to cite by time in a movie, etc., in case one of those other formats already does what you need in the style you want. I don't imagine anyone would be using "page" for an Audio Recording, for example, so maybe there's already some option in an existing style.