The ability to conceive time is a corner stone of human cognition. It is unknown, however, whether time conceptualisation differs depending on language of operation in bilinguals. Whilst both Chinese and English cultures associate the future with the front space, some temporal expressions of Chinese involve a configuration reversal due to historic reasons. For instance, Chinese refers to the day after tomorrow using the spatiotemporal metaphor hou-tian - 'back-day' and to the day before yesterday using qian-tian - 'front-day'. Here, we show that native metaphors interfere with time conceptualisation when bilinguals operate in the second language. We asked Chinese-English bilinguals to indicate whether an auditory stimulus depicted a day of the week either one or two days away from the present day, irrespective of whether it referred to the past or the future, and ignoring whether it was presented through loudspeakers situated in the back or the front space. Stimulus configurations incongruent with spatiotemporal metaphors of Chinese (e.g., "Friday" presented in the front of the participant during a session held on a Wednesday) were conceptually more challenging than congruent configurations (e.g., the same stimulus presented in their back), as indexed by N400 modulations of event-related brain potentials. The same pattern obtained for days or years as stimuli, but surprisingly, it was found only when participants operated in English, not in Chinese. We contend that the task was easier and less prone to induce cross- language activation when conducted in the native language. We thus show that, when they operate in the second language, bilinguals unconsciously retrieve irrelevant native language representations that shape time conceptualisation in real time.