Assistance needed with Breaksheet

Good morning everyone,

First time posting and I tried searching but unable to find what I'm looking for. If I missed it please direct me to the correct location.

I'm creating a breaksheet for my location. I'm having a hard time getting the cells to calculate from each other. Here's what I'm trying to do:
A1 = # of hours of the shift for example 8.5
B1 = the start time of the shift 5:45
C1 = Break #1 30
D1 = Break #2 30
E1 = B1+A1

It seems easy but here's the issue. B1 is formatted 0\:00 and I cannot get it to calculate based off of cell A1 which is a general number. Should I format A1 to represent the number of hours in minutes?

My next issue is, is there a way to have it determine how many breaks that row will allow? For example for C1 and D1 for it to enter in a 0 / 15 / 30 based off of the number of hours entered in cell A1.

Below is a grid we follow for breaks.
Hours Worked Lunch Breaks
0.0-6.25 0 15
6.50-8.25 30 15
8.50-10.25 30 30
10.50-13:25 30 15 30
13.50-14.75 30 30 30
15.00 + 30 30 30 30


Thank you in advance and any assistance would be amazing!!!