one day

(rare) the first day of the month

a year

(a duration of) one year / an unspecified year in the past

A solar year, the time it takes the Earth to complete one revolution of the Sun (between 365.24 and 365.26 days depending on the point of reference)

one day, 24 hours / the daytime, the period from dawn until dusk / (figuratively) a short period of time / one day, someday, an unspecified day / the first day of the month

all day

the first day of the month (solar or lunar calendar)

(obsolete) one day, 24 hours / (obsolete) the daytime, the period from dawn until dusk

(rare, obsolete) (all senses appear to be identical as for hitohi above)