The phrase 'on a clock' is correct and usable in written English.
It is typically used to refer to the hands of an analog clock, as in "The minute hand was on the 5 when I looked at the clock."
A smattering of Syrian flags, one planted on a clock tower, flew amid the destruction as government soldiers fanned through the streets.
During maneuvers from one target to the next, Chandra slews more slowly than the minute hand on a clock.
I see the hours on a clock ticking away.
It takes the minute hand on a clock 15 minutes to slew 90 degrees.
"I think of him every time I see 9-11 on a clock".
A Thomson Reuters spokesman blamed the problem on a "clock synchronization issue".
In most film sequences, the camera lingers on a clock for a few seconds.
They were quite intense sessions, everything was on a clock, everything was done for a reason.
The monuments form a circle around Flagstaff like the hours on a clock.
The number buttons are arranged in a circle, like the numbers on a clock.
Your clock's been turned to zero, though there is no zero on a clock.
