Both DMY and HMS are sensical notations of time. For most people the day is the most important part of the cycle in a year. We measure most of our actions and chores in days then months then years. In a meeting, in official letters, taxes etc. everything is specified in days.

Similarly hour is the most common division of a day. Generally humans have an internal tendency to measure things in half of an hour interval and hour is the closest one. One usually rents a parking slot for integer multiples of an hour. The travel distances are specified in hours or fractions of it

Putting the most important measure at first just makes sense.