At my college radio station, every applicable record had intro time cues written on a label on the record jacket. You would know that there was, say, seven seconds you could talk over before the song began in earnest. "Hitting the post" (not familiar with the term) was not really a problem for the deejays. p.s. - I loved being able to inject our call letters into the gap on 'Riders On the Storm', timed to the top or bottom of the hour.