One
A company might have executives setting policy and strategy, engineers designing products, managers handling personnel and others handling various functions. They all do different things -- but if they're doing them with a shared underlying purpose, the company -- and the individuals in it -- will likely be successful. The Lord wants all human society to function in a similar way. We have different skills and individual loves, but if we all share a mutual love -- a love of serving others -- then society will function as one, will be a reflection of heaven and will be a good receptacle for the Lord's love. This can also happen within each of us, as we unify our talents and ideas around a central love. And in an abstract sense, it illustrates how a wide collection of varying ideas can be unified around a shared good intention. That is the kind of love pictured when “one” is used in the Bible, either as a specific number or in the sense of several people or objects “being one.” In more casual references -- when used to identify a specific person or object -- the meaning is relatively literal, and is connected to that person or object.
Day
Like other descriptions of time in the Word, "a day" or a number of "days" describe a spiritual state rather than our natural concept of time. A spiritual "day" describes a state of mind or a state in our relationship with the Lord rather than a 12-hour or 24-hour span of natural time. "Day" describes a state in which we are turned toward the Lord, and are receiving light (which is truth) and heat (which is a desire for good) from the Lord.