Parashas Naso · Passuk 6:08
throughout their term as nazirite they are consecrated to GOD.
Chabad.org — English translation + Rashi
Source: Nazir 47a.
English: “All the days” — this teaches that there is no naziriteship for hours.
In context: A nazirite vow must be for a period measured in days (minimum thirty by rabbinic standard); a vow for mere hours is not effective as nezirut.
Custom
Chazal derive that naziriteship cannot be vowed for a period of hours only.