Here are some possibilities you could use, depending on the context:
Formal/Descriptive:
* A collection of clocks
* A display of clocks
* A set of clocks
* An array of clocks
Informal/Humorous:
* A tick-tock
* A timepiece ensemble
* A chime of clocks
Ultimately, the best collective noun will depend on the specific situation and what you want to emphasize.