Writing has long been considered to be one of the most complex language skills for language learners to master. To help students develop this skill, many studies have been devoted to exploring potential factors affecting student writers’ performance, such as the effect of pre-planning tasks. Among the many other factors examined, however, the sheer effect of time on students’ writing performance is rarely studied. This is particularly true in the educational context of Taiwan, where English is mostly learned as a foreign language (EFL). The understanding of Taiwanese EFL students’ linguistic performance in terms of writing complexity is especially limited. To shed light on this research gap, this study explores the effects of time factors on a group of 42 Taiwanese EFL students’ writing complexity. The participants involved were required to complete two sets of timed writing tests: (1) 20 minutes versus 40 minutes, and (2) 30 minutes versus 50 minutes. In total, they produced 168 writing samples for analysis, for which both inferential and descriptive statistics were employed. The study results show that time factors play an important role in Taiwanese EFL students’ writing complexity. Specifically, with greater time resources, Taiwanese EFL students write with more complexity than those with less time resources. This study concludes by providing discussions and identifying possible reasons for further studies.