How do I sort by day?
This could be working for example if you'd use a taxonomy term reference instead of a text field. Just create a taxonomy with your workdays as terms. 


use these tags on your content
in views add a field to show the term your content is tagged with
in the format options choose 'group by' and select your taxonomy field


Now the content should be grouped by the workdays. To achieve the correct sorting order you can either rely on the term-ID (which is created in chronological order) or just arrange your terms with drag and drop (in the terms dialog).