What is the minimum time required for an unqualified vow of I'tikaf?

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If one vows I'tikaf absolutely, the minimum time that can be called I'tikaf is required, even if only an hour of night or day, unless the opinion requiring fasting for I'tikaf is adopted, in which case a full day is required. A mere glance or time insufficient to be termed I'tikaf is not acceptable under either ruling.