Quantum computers can be seen as "quantum accelerators" attached to a classical computer.
The application of quantum gates is a problem of sending signals to the quantum device/accelerator.
The classical aspect of signal sending is clocked by the classical computer. The speed of the quantum machine is determined:
relatively: to the worst case complexity of executing the algorithm on the classical machine instead of the quantum one (imagine using a CPU instead of the quantum accelerator)
exactly: time needed to run the algorithm on the quantum accelerator
The latter depends on the "gate times" of the accelerator.
Therefore, a quantum computer is clocked in multiple ways:
However, the clock speed does not play a significant role to why quantum machines seem for particular algorithms more powerful.