Regulations Regarding International Students Undertaking Studies in Taiwan Article 11

An international student who reports to register at a university or tertiary college, a five-year program at a junior college, or a senior secondary school, junior high school, or an elementary school before it is already one-third of the way into the first semester of the current academic year shall be registered for the first semester. If it is already more than one-third of the way into the first semester, the international student shall register for the second semester or the next academic year. However, this restriction does not apply if the competent authority has some provision that overrides it.
中文原文 外國學生來臺就學辦法第11條
大專校院、專科學校五年制、高級中等以下學校之外國學生註冊入學時,未逾該學年第一學期修業期間三分之一者,於當學期入學;已逾該學年第一學期修業期間三分之一者,於第二學期或下一學年註冊入學。
但各主管機關另有規定者,不在此限。

English translation for reference only; the Chinese text prevails. Not legal advice.