The word "day", when used without any limiting words, may refer to a long or prolonged period: as, the "day of grace", the "day of visitation", the "day of salvation", the "day of judgment", the "day of the Lord", "man's day", &c. But when the word "day" is used with a numeral (cardinal or ordinal), as one, two, three, &c., or first, second, third, &c., "evening and morning" (Gen. 1), or the "seventh day" (Ex. 20:9, 11, &c.), it is defined, limited, and restricted to an ordinary day of twenty-four hours.
The word "day" is never used for a year. Sometimes a corresponding number of days is used for a corresponding number of years, but in that case it is always expressly stated to be so used; as in Num. 14:33, 34. But, even in these cases, the word "day" means a day, and the word "year" means a year. It is not said that a day means a year; but the number of the forty years is said to be "after the number of the days in which ye searched the land, even forty days".
It is the same in Ezek. 4:5, where the years of Israel's iniquity were laid on Ezekiel "according to the number of the days". In this case also, the word "days" means days, and the word "years" means years.
There is no Scriptural warrant for arbitrarily assuming this to be a general principle in the absence of any statement to that effect.