The calendar of the date field in Zendesk Support starts the week on Sunday. Can the calendar start the week on Monday instead?
The calendar that prompts when you click a date field always starts the week on Sunday. It is not possible to change the beginning of the week to another day.
To use a date field in your triggers, see When using a custom date field as a trigger condition, what does "is within the previous" and "is within the next" do?.