Probably went with the simplest implementation, if starting from the current “seconds since epoch” value. Let the user do any calculations needed to translate three days into that measurement.
It also efficiently annoys the most people at once: those what want hours will complain if they set it to days, thought that want days will complain if hours are used. By using minutes or seconds you can wind up both segments while not offend those who rightly don't care because they can cope with a little arithmetic :)
Though doing what sleep(1) does would be my preference: default to seconds but allow m/h/d to be added to change that.
Hence the way I would do it (and have for other purposes), as stated in my final sentence. Have the human state the intent and convert to your own internally preferred units as needed.
No no no, see now we just say "computer! do tedious math!", and it will do some slightly different math for us and compliment us on having asked it to do so.
The one true unit of time is hexadecimal encoded nanoseconds since the unix epoch. (I'm only half joking because I actually have authored code that used that before.)
It also efficiently annoys the most people at once: those what want hours will complain if they set it to days, thought that want days will complain if hours are used. By using minutes or seconds you can wind up both segments while not offend those who rightly don't care because they can cope with a little arithmetic :)
Though doing what sleep(1) does would be my preference: default to seconds but allow m/h/d to be added to change that.