ViewType = WorkWeek -> Days=1 and StartDate not monday

To get the calculated start/end you can use visibleStart() and visibleEnd() methods:

https://api.daypilot.org/daypilot-calendar-visiblestart/
https://api.daypilot.org/daypilot-calendar-visibleend/

The viewType property (https://api.daypilot.org/daypilot-calendar-viewType/) doesn't change startDate (https://api.daypilot.org/daypilot-calendar-startdate/) and days (https://api.daypilot.org/daypilot-calendar-days/) values.

ok, thanks for the hint. this did the trick.

in the link about _viewType_ you provided there is a link to the different _viewTypes_ (https://doc.daypilot.org/calendar/view-types/) and there it says:

These modes simplify work with the standard views.
It automatically sets the Day property value.
It automatically sets the StartDate to the first day of week in WorkWeek and Week modes (using the current culture).