One division of the Hora spans 15 degrees, half a sign, and there are twenty four of them in the zodiac. The ascendant crosses fifteen degrees in roughly an hour, so of all the divisional charts the D-2 is the least sensitive to a doubtful birth time. A person who knows the hour but not the minute still has a usable Hora.
The D-2 is also the odd one out in the scheme, and the reason is worth stating plainly. In the Parashari rule the two halves of a sign are not assigned to two of the twelve signs. They are assigned to the Sun and the Moon, so a planet in the D-2 falls in a solar half or a lunar half and nowhere else. Some astrologers therefore decline to cast the Hora as a chart at all and read it only as a two-way classification bearing on wealth and sustenance, while others map the solar half to Leo and the lunar half to Cancer in order to produce something a chart-drawing program can display. Those two practices give different-looking output from identical longitudes, and a reader comparing two Hora charts should establish which convention is in front of them before concluding anything.
Despite that irregularity the Hora sits in all four classical groupings, the shadvarga, saptavarga, dashavarga and shodashavarga, on the strength of its subject matter rather than its structure.