Lev 23 assumes the month begins on a Sabbath.
Lev 23:5 In the first month, on the fourteenth day of the month, at twilight,is a Passover offering to the Lord. 23:6 Then on the fifteenth day of the same monthwill be the festival of unleavened bread to the Lord; seven days you must eat unleavened bread. 23:7 On the first day there will be a holy assembly for you; you must not do any regular work.
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23:24 “Tell the Israelites, ‘In the seventh month, on the first day of the month, you must have a complete rest, a memorial announced by loud horn blasts, a holy assembly. 23:25 You must not do any regular work, butyou must present a gift to the Lord.’”
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23:35 On the first day is a holy assembly; you must do no regular work. 23:36 For seven days you must present a gift to the Lord. On the eighth day there is to be a holy assembly for you, and you must present a gift to the Lord. It is a solemn assembly day;you must not do any regular work.
Lev 23:5 In the first month, on the fourteenth day of the month, at twilight,is a Passover offering to the Lord. 23:6 Then on the fifteenth day of the same monthwill be the festival of unleavened bread to the Lord; seven days you must eat unleavened bread. 23:7 On the first day there will be a holy assembly for you; you must not do any regular work.
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23:24 “Tell the Israelites, ‘In the seventh month, on the first day of the month, you must have a complete rest, a memorial announced by loud horn blasts, a holy assembly. 23:25 You must not do any regular work, butyou must present a gift to the Lord.’”
...
23:35 On the first day is a holy assembly; you must do no regular work. 23:36 For seven days you must present a gift to the Lord. On the eighth day there is to be a holy assembly for you, and you must present a gift to the Lord. It is a solemn assembly day;you must not do any regular work.
Joh 19:31 The Jews therefore, because it was the preparation, that the bodies should not remain upon the cross on the sabbath day, (for that sabbath day was an high day,) besought Pilate that their legs might be broken, and that they might be taken away.
The Sabbath being referred to here is the First Day of Unleavened Bread and it occurs on the fifteenth day of the first month.
The weekly Sabbath is always on the seventh day of the week...
Lev 23:2 Speak unto the children of Israel, and say unto them, Concerning the feasts of the LORD, which ye shall proclaim to be holy convocations, even these are my feasts.
Lev 23:3 Six days shall work be done: but the seventh day is the sabbath of rest, an holy convocation; ye shall do no work therein: it is the sabbath of the LORD in all your dwellings.
Exo 20:8 Remember the sabbath day, to keep it holy.
Exo 20:9 Six days shalt thou labour, and do all thy work:
Exo 20:10 But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates:
Exo 20:11 For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it.