the top of the hour
The beginning of an hour (e.g. 7:00), as opposed to the bottom of the hour (e.g. 7:30). And we'll bring you that news story at the top of the hour.
the top of the ˈhour
(especially American English) (on a TV/radio programme, etc.) the beginning of an hour on a clock: We have more news coming up at the top of the hour. OPPOSITE: the bottom of the hour