Hi Nick,

You need to add the results you expect in columns C&D since it's not obvious from your post exactly what you require. You should also add notes explaining how you arrive at the results.

For instance when you say no breaks should overlap do you mean for each employee only or across all employees? In which case who takes precedence.
Using terms like 'at least' is no help when constructing a formula since it's open to interpretation.
Exactly how are the unavailable times to be used? Do you mean a break can't start within the unavailable time. Can they start a break before the unavailable time but which runs into the unavailable time?

Do employees work past midnight, i.e. is the time out less than the start time but on the next day?