The days considered 'workday' can vary in different cultures; some include Saturday. In many Middle Eastern countries, Sunday is part of the typical workday.
Pro Tip 2/3
Not Always 9-5
'Workday' may not be 9 am to 5 pm for everyone, especially in shift work or with flexible hours. My workday starts at noon since I work the second shift.
Pro Tip 3/3
Hyperbole Usage
Used hyperbolically to mean a very long day of work, even if it's not an entire day. I have a workday ahead just to finish this report.