This article presents an acoustic study of the acquisition of vowel formant dynamics in L2 (Southern British) English by Polish learners at two levels of proficiency, along with baseline data from L1 English and L1 Polish. Results from our experiment suggest that the acquisition of English vowels by Polish learners entails a temporal reorganization such that vocalic targets in English are housed later in a vowel's duration than they are in Polish or Polish-accented English. This leads to an increase in the degree of formant movement through the 20%-40% portion of vowel duration with increased English proficiency. Implications of these findings for cross-language phonetic similarity, a crucial concept for current theoretical models of L2 speech, are also discussed.