Numbers 9:2-3

9:2 “The Israelites are to observe the Passover at its appointed time. 9:3 In the fourteenth day of this month, at twilight, you are to observe it at its appointed time; you must keep it in accordance with all its statutes and all its customs.”

Numbers 28:2

28:2 “Command the Israelites: ‘With regard to my offering, be sure to offer my food for my offering made by fire, as a pleasing aroma to me at its appointed time.’