Regarding the expressions of time limits or some quantities as an object of prepositions, is it possible to make a generalization such as below?
"If the reference point is the point of arrival , include it. If the reference point is the starting point, do not include it (they constitute comparisons)"
Under these rules, objects of “until” and “by” are arrival points, so the referenced points are to be included, but these of “before”, they are starting point and to be excluded. For example,
by / till April 1 -> Including April 1.
before April 1 -> not including April 1