<p>Found this on multiple grammar sites: </p>
<p>When means at that moment, at that time, etc.. Notice the different tenses used in relationship to the clause beginning with when. It is important to remember that when takes either the simple past OR the present the dependent clause changes tense in relation to the when clause.</p>
<p>So in the 1960s or the specific year, can't remember which, musicians began to reach an international audience. AT THAT TIME, 1960 or whatever year it was, musicians began to reach an international audience.</p>