When was worship commanded for Sabbaths?
Many times throughout the Bible.
Worship is a personal thing that you can do any time. We should worship God every day of the week.
The issue is obediance.
God said "remember the sabbath to keep it Holy". If you say, "no, I'm going to forget that day and keep another", that would be disrespectful, disobedient and the opposite of worship.
Jos 24:14 Now therefore fear the LORD, and serve him in sincerity and in truth: and put away the gods which your fathers served on the other side of the flood, and in Egypt; and serve ye the LORD. 15 And if it seem evil unto you to serve the LORD, choose you this day whom ye will serve; whether the gods which your fathers served that were on the other side of the flood, or the gods of the Amorites, in whose land ye dwell: but as for me and my house, we will serve the LORD.
.1Ki 18:17 And it came to pass, when Ahab saw Elijah, that Ahab said unto him, Art thou he that troubleth Israel? 18 And he answered, I have not troubled Israel; but thou, and thy father's house, in that ye have forsaken the commandments of the LORD, and thou hast followed Baalim....21 And Elijah came unto all the people, and said, How long halt ye between two opinions? if the LORD be God, follow him: but if Baal, then follow him. And the people answered him not a word.
Not keeping Sabbath was a law introduced in the dark ages and keeping Sunday was a tradition of the dark ages. (See post 62)
Gods commandments have not changed.
1Jn 5:3 For this is the love of God, that we keep his commandments: and his commandments are not grievous.