During speaking, the mental lexicon is accessed (i) to select the necessary words, and (ii) to retrieve their phonological and syntactic patterns. However, the nature of real-time activation of words and phonological rules is largely unknown. In Hungarian, voicing assimilation is a relatively strong phonological process prevailing both within and across words. While a lot is known about its phonological nature as well as its phonetic outcome, the temporal patterns of its implementation during speech production have not been analyzed yet. This paper deals with the temporal coding of voicing assimilation (i) in language acquisition, (ii) in spontaneous speech (of subjects of various ages), and (iii) in repetition tasks. Results show that (i) by the age of 4 Hungarian-speaking children acquire this phonological rule without mistakes, (ii) in spontaneous speech successful voicing assimilation depends on certain time limits partly depending also on the total temporal organization of speech coding, and (iii) without the higher-level semantic and syntactic organization of speech (shadowing task), subjects are not able to plan the encoding of voicing assimilation processes as securely as they do in spontaneous speech.