on the stroke of seven/nine etc
From Longman Dictionary of Contemporary Englishon the stroke of seven/nine etcon the stroke of seven/nine etcEXACTTIME/AT A PARTICULAR TIMEat exactly seven o’clock etc She arrived home on the stroke of midnight. The only goal of the match came on the stroke of half time. → strokeExamples from the Corpuson the stroke of seven/nine etc• Arthur would be gone on the stroke of nine, and Ann too, if it was possible.