For a good discussion, instead of looking at the problem strictly programmatically, you could look at it as something you could map in vector space.

The dimensions of appointments are [startTime, endTime, location]. If you have points in one appointment that intersect with other appointments, then you have a collision.

This problem is solved with a couple of simple if statements. Finding a "solution" that is more complex than necessary or introduces knowledge that really isn't needed is the sign of a programmer who... over-engineers and is likely to be a detriment.