Time differences without dates?

I've been searching but I cannot seem to find information about this. I've attached an image link to my current worksheet.

I'm creating a new employee schedule for a restaurant. Many days, employees have two shifts (morning and evening). The sheet does not include dates, so the time difference calculations aren't working very well. If I attempt to calculate the total hours for one day, it works fine. However, if I attempt to include multiple days into one cell's formula, it gives me an erroneous number. Where should I begin?

Here's a link to the image. hosted on Imgur.

Thank you in advance for your help!

Thank you so much! I'm going to mark it as resolved.