Contrasting proposals of an early emergence, Tom Güldemann has argued that less time may have been required for the divergence than is usually assumed, as it is possible for a language to rapidly restructure due to areal contact, with the evolution of Chadic (and likely also Omotic) serving as pertinent examples.
kəntɹˈæstɪŋ pɹəpˈoʊzəlz əvən ˈɜːli ɪmˈɜːdʒəns, tˈɑːm ɡˈuːldᵻmən hɐz ˈɑːɹɡjuːd ðæt lˈɛs tˈaɪm mˌeɪhɐv bˌɪn ɹᵻkwˈaɪɚd fɚðə daɪvˈɜːdʒəns ðɐn ɪz jˈuːʒuːəli ɐsˈuːmd, ˌæzɪtˌɪz pˈɑːsᵻbəl fɚɹə lˈæŋɡwɪdʒ tə ɹˈæpɪdli ɹᵻstɹˈʌktʃɚ dˈuː tʊ ˈɛɹiəl kˈɑːntækt, wɪððɪ ˌɛvəlˈuːʃən ʌv tʃˈædɪk ænd lˈaɪkli ˈɔːlsoʊ ɑːmˈɑːɾɪk sˈɜːvɪŋ æz pˈɜːtɪnənt ɛɡzˈæmpəlz.