Sabbatarians, including SDA, insist that the day to worship God is Saturday. Strictly speaking, it is Friday evening to Saturday morning. They claim that the early churches met on the Sabbath and that the Roman Catholic organisation introduced Sunday worship. Both claims are false.
There is historical and Biblical evidence that refutes the Sabbatarian claim. Sunday is the first day of the week and the day that he Lord Jesus rose from the dead. The Apostle John is the only direct statement regarding the Lord's day, Revelation 1:10.
The day of the Lord refers to a specific day in Jewish eschatology that was the day that John was seeing in his vision, not to the day of the week that he happened to have it.
Nowhere does it state in the NT that believers met strictly on the Sabbath. Believers met on the first day of the week:
Indeed, there is nothing about the command to keep the 7th day holy that prohibits meeting on other days of the week.
"On the first day of the week we came together to break bread. Since Paul was ready to leave the next day, he talked to them and kept on speaking until midnight." Acts 20:7
Part of sanctifying a period of time involves distinguishing between when it begins and ends, so Jews have a tradition of meeting on the first day of the week on Saturday night at sundown for Havdalah in order to mark the transition between the Sabbath and the work week. So Paul did not speak from morning until midnight but rather he spoke from sundown until midnight, then left on Sunday morning to travel. So this does not establish that they met on Sunday morning, and even if they had, it does not establish that it was the start of the new tradition, and even if it was, it does not establish that they hypocritically set aside God's command to keep the 7th day holy in order to establish their own tradition, and even if they had, then this would not establish that we should follow their example of sin.
"On the first day of every week, each of you should set aside a portion of his income, saving it up, so that when I come no collections will be needed." 1 Corinthians 16:2
Jews also traditionally don't handle money on the Sabbath, so waiting until Havdalah to collect offerings is in according with continuing to keep the Sabbath holy. If they had collected an offering on the Sabbath, then you would have something supporting your position.
Lord Jesus said that the Sabbath was made for man. The Lord's day is just that, the “Kyriake hemera,” i.e a day belonging to the Lord.
Indeed, the Sabbath is a precious gift from God that was made for our own good and not for our detriment, so we should not spurn it.
It is interesting that the emphasis on the Sabbath for Israel was as a day of rest. Israel was fundamentally an agricultural society. 6 days of hard work was to be followed by complete rest. The "sabbath rest" for the believer is no longer physical. It is entering into the finished work of Christ on the cross, allowing Him to live out His life in and through us. Lord Jesus is no longer limited by a physical body. He dwells in the heart of every believer to lead, direct and empower us to do God's will.
Nowhere does the Bible say that the Sabbath rest for the believer is no longer physical. In Hebrews 3:17-18, they did not enter into God's rest because of their disobedience/unbelief, and in Ezekiel 20:13, it specifically mentions that they greatly profaned God's Sabbaths, so someone should not think that they can enter into God's rest while having the same disobedience/unbelief that preventing the Israelites from entering into God's rest. In Hebrews 4:9-11, there remains a Sabbath rest for the people of God, we should rest from our work as God rested from His, and we should be careful to enter into that rest so that no one might fall away by the same sort of disobedience, so we should continue to keep the 7th day holy.
As humans, we are still restricted by our bodies. My body reminds me of this every time I get out of bed. I have a slight ache or pain here and there incurred simply by sleeping. Ridiculous. Everyone needs a day of rest. And in modern times when work is so varied, rest can be different things to different people. Someone tied to a computer all day should get out and about and enjoy physical activity. A builder or a bricklayer will want to have a physical rest. Godly common sense is a great asset!
God could have commended to take a day of rest once a week if that is what He wanted, but He commanded to rest on the 7th day in memorial of when He rested after Creation. There is no evidence in the Bible of people picking which day they wanted to rest on or of picking what rest means to them.
It was not Rome that introduced the "Lord's Day" as the time for believers to meet. Rome did formalise it. It was common practice long before Constantine.
In Mark 7:6-9, Jesus criticized Pharisees as being hypocrites for setting aside the commands of God in order to establish their own traditions, so there is nothin inherently wrong with following a tradition of meeting on Sunday mornings in addition to obeying God's command to keep the 7th day holy, but we should not hypocritically set aside any of God's commands in order to establish our own traditions.