Ivan, If I may try to summarize, There are 'regular' Sabbath days, which are every seventh day, the ending of every week...and we are to keep them holy. Whether a Sabbath Day begins at sundown after the sixth day, or whether it begins at sunrise of the seventh day is part of our discussion here. I think Off Grid suggests it begins in the morning of the seventh day, but, many think it begins at sundown the previous evening.
The first day of every month is also being discussed. Off Grid is suggesting that a month begins when the moon is full, (renewed) not, as is practiced by others, at the first sighting of the renewed sliver. This affects when the Feast Days are to be kept. Because, obviously (I hope) the tenth day of say, the seventh month, would depend on when the month started. In these two versions of when the month begins, the tenth would occur two weeks apart from each other. Which is the right day, then, to keep that special Sabbath, wherein we are to "afflict" ourselves.
Or, the First month Feasts of Passover and the Feast of Unleavened Bread. They depend on when, actually, the first day of the month starts, because ten days later a lamb is picked, and killed on the fourteenth, and at even, the First Day of Unleavened Bread occurs on the fifteenth of that month. Comparing these two methods of dating the first day of the month would result in Passover and the feast of Unleavened Bread would be two weeks apart from each other. (The two differing methods of determining when the month started)
Some of us didn't even realize there was any problem determining the days that God wants us to keep "special", but, apparently, there are many ways....so, we must ask our Father to teach us and clarify the truth so we may become unconfused and follow His instructions as He declares....because we love Him and want to do things His way, not according to the world's way. Certainly, we will be peculiar to the world, but, so what? We are in the world, but not of it. God bless you.