We have changed the first day of the week setting to Sunday so that our calendars match the others we use when selecting dates, etc. This puts Sunday first, and Saturday last on a row in calendar views.
However, now when we are in Timeline view on a board Sunday and the next 4 days are white and Friday and Saturday are greyed out as if they are the weekend. Saturday and Sunday are still our weekend but we prefer the format of having Sunday as the first day of the week. Maybe there needs to be two settings, one for the visual first day of the week on calendars and timelines, and one for the first day of the work week.