What is the Sabbath?
Why am I unavailable on Sabbath - currently Friday (night time) and Saturday (day time)
The 7th day Sabbath is fixed and perpetually recurring. It is only the Calenders and Rosters mankind makes that want you to 'wander' from and cause you to work on "The 7th Day".

The seventh day of the current Georgian weekly calendar cycle is NOT the same as the "7th Day Sabbath" cycle of the fourth commandment of the LORD GOD in Heaven.
People who observe the "7th Day Sabbath" DO NOT do this on the day called Saturday, they do it on which ever calendar day the "7th Day Sabbath" would actually fall.
Saturday in the current Gregorian calendar seven day weekly cycle just happens to coincide with the "7th Day Sabbath" seven day Sabbath cycle.
 

In most places Saturday is a day considered as a weekend day off work, or can be negotiated with an employer as a recurring non-work day.  Or if rostered as a work day, a worker can swap with a colleague who does not mind working that day if not already rostered to work that day.  So with negotiation with employers and work colleagues it may be possible to secure time off work to observe the "7th Day Sabbath".
 

With sliding Roster systems becoming more prevalent which have an alternate cycle that enforces a schedule of non-work days off falling on week days and not the Gregorian non-work weekends of Saturday (and Sunday) this will make negotiations to observe the "7th Day Sabbath" very difficult.
 

However any new Calendar change which includes any additional days outside of the seven day weekly calendar cycle will cause the "7th Day Sabbath" to appear on a different work day each year that passes through that new calendar.  Making it practically impossible to keep the "7th Day Sabbath" in two easy steps.
 

The implementation of such Calendars can be obscured as a necessity based on business and economic reasons rather that religious reasons.  Business work hours and days being given priority over religious observance days off.
 

1. First change all Diaries and Calendars so that the business day of Monday becomes the first day of the week.
This will make Saturday in the Gregorian calendar appear as the sixth day of the calendar week. The "7th Day Sabbath" will continue to coincide with Saturday in the weekly calendar cycle, as they both rely on their own seven day cycle.  This should not affect people who observe the "7th Day Sabbath" because they may still be able to negotiate time off work with employers or work colleagues.
 

This change has already been implemented by ISO 8601 - https://www.iso.org/iso-8601-date-and-time-format.html
 
Sunday then appears as the seventh day of the weekly Calendar cycle however this is NOT the same as the seventh day of the "7th Day Sabbath" seven day Sabbath cycle.
This is Happening, Sunday laws, No buy no Sell ? SDA Wake up
 

2. In addition to making each week start with Monday, make each Year of the new Calendar begin with Monday as the first day of each and every future year.
The reasoning for this can be obscured on business accounting reasons that quarterly reports for each year and following years need to be compared directly and exactly, requiring the same number of days in each quarter.
This can occur if the days in each month and consequent quarters agree with additional days added outside the regular weekly calendar cycle to enable the next year to start on a Monday. 
 

Click on this link and scroll up and down the yearly calendars to see how the Gregorian calendar could be replaced with a World Calendar.