Google Sheets hours worked before and after specified time

I am trying to specify a time that starts a shift premium for a time card. I was so happy I finally figured out how to get it, but then I changed a time to a first shift time and thats when I lost all hope. I have spent hours messing with this and my current formula's looks like

x1.05

 =IF(COUNT(A20:B20)=2,MOD($B$18-A20,1)*24,"")

x1.1

 =IF(COUNT(A20:B20)=2,MOD(B20-$B$18,1)*24,"")

My end goal is to have it so first shift (7am - 3pm) fall under base pay, 2nd shift (4pm-12am) fall under x1.05 and anything past 12am falls under x1.1

Just getting this far has been a mind blower for me and any help would be greatly appreciated.

I have moved this to its own sheet to share with everyone. I am still playing with things myself and trying different things, but on the sheet I have included the variables along with the wording of the contract that effects the pay scale. NOTE the times I originally provided were just examples from the top of my head.

My Sheet