You’re missing almost all of it.
Watching for the new moon of the 7th month was already an ancient tradition by the time Yeshua was born.
The appearance of the moon was an unpredictable event, due to the fact that the weather also played into its visibility, which could cause a day of delay.
Yom Teruah is the only feast that occurs on the new moon, thus the traditional phrase regarding it: “No man knows the day nor the hour.”
Yeshua was telling his disciples exactly which feast would mark his coming for them “in the spirit.”
Could you then post the relevant Scriptures?
Could you point out other places where this 'traditional phrase' is used?