It also deals with the problem of the bounds on the ranges (open-closed, open-open etc) implicitly in a way which is harder to mess up.
One complication it's potentially missing is exactly who's days we are talking about i.e. is it days starting in GMT or UTC or EST or whatever the 'suppliers' or the 'customers' timezone is, are we actually talking about some day concept perhaps from start of business. Representing this as a datetime start / end certainly makes it possible to represent these concepts, if perhaps not making anything else particularly easier.
One complication it's potentially missing is exactly who's days we are talking about i.e. is it days starting in GMT or UTC or EST or whatever the 'suppliers' or the 'customers' timezone is, are we actually talking about some day concept perhaps from start of business. Representing this as a datetime start / end certainly makes it possible to represent these concepts, if perhaps not making anything else particularly easier.