No One Knows the Day or the Hour?

Christians over the centuries have separated themselves from their Hebraic
roots causing the misunderstanding of key Jewish biblical idioms. An idiom
is also a figure of speech. When Y'shua (Jesus) uttered His famous words
concerning the Messianic Era in Mattityahu (Matthew) 24:26, "No one knows
about that day or hour, not even the angels in Heaven, nor the Son, but
only the Father", He used a common Jewish figure of speech referring to a
specific Jewish Festival. In essence He was saying, "I am coming for My
Bride on such and such a day! Be watching!" What day could the Jewish idiom
be referring to?