You need to input the list in a [key]|[value] format like this:
1|Monday
2|Tuesday
3|Wednesday
4|Thursday
5|Friday
6|Saturday
7|Sunday
This would render as
<option value="1">Monday</option>
<option value="2">Tuesday</option>
... and so on.
Hope this helps.
BTW, the logic can be found in easy-post-types/classes/custom-select/custom-select.php in the function prepareArray().
If you want to use PHP the generate the list, your code needs to return an array like this:
return array(
array(1, 'Monday'),
array(2, 'Tuesday'),
... and so on.
);
