I set the DayRangeSettings.NumberOfDays to 1 and after that the DayRangeSettings.VisibleDays to 1 in the properties window.

When you then look at the designer class it says:
DayRangeSettings.NumberOfDays = 1;
DayRangeSettings.VisibleDays = 1;

Because the default for VisibleDays = 7 and NumberOfDays is set before VisibleDays it throws an exception: Specified argument was out of the range of valid values. Parameter name: '1' is not a valid value for 'NumberOfDays'. 'NumberOfDays' must be greater than or equal to 'VisibleDays'.