The calendar widget does not respect the locale configured in Jira, and therefor it's not possible to change the first day of the week. This is because we're currently utilizing the atlaskit-datetimepicker, which defaults to a week starting on Sunday (weekStartOfDay as 0/Sunday).

To resolve this issue we'll need to add an option for ProForma to query the application property jira.date.time.picker.use.iso8061. This will allow us to properly configure the weekStartOfDay for the DateTimePicker.