I can’t find any setting for changing first day of week to monday, is this trivial to implement if missing? 
Another issue is that that time & date entry is broken, if it’s an all day event there should be an option to select it before the time entry fields mess up the dates, and the dates seem to change randomly when editing.
Also noticed that it’s possible to enter 00:00 in both time & date, (which sometimes works, sometimes doesn’t) leading to calendar giving an error which will then cause some conflict with drafts leading to a repeated 422 error until the page is rolled back to an earlier revision, then re-edited etc.