Formula to Calculate Downtime

I have an issue with a formula. On the "Weekly Results" tab, I have two separate rows (13 & 23) that need to calculate total downtime. The caveat is that the total downtime is contingent upon the total shift (rows 14 & 24). I thought it was going to be as simple as subtracting the shift from the total load time (rows 15 & 25), but alas, it is not. Basically, the total downtime is the total shift minus the total load time. The issue I'm running into is the fact that if first shift starts early (i.e. 12 hour shift) then the downtime needs to reflect that based on the load start time on the day of the week tab. The other issue is second shift. Second shift has a firm start time, but not a firm end time. If they work over, then the formula needs to be able to find the last load of the day, and then reflect the last load time to the shift end time in the total downtime. I'm at a loss. I've included the actual spreadsheet as it has no confidential info in it. It's the only formula I'm stuck on. I don't care if there are helper columns or not. I can hide those.

Please let me know if I didn't do a good job of explaining.