There are linear and rotary molecular motors in the cells. Do any of them have a fixed or stable frequency or speed?
There are molecular motors but the frequency is a function of energy input (ATP); similar to the angular velocity dependence on amount of current in electrical motors. 

The concept of molecular motor may not be suitable for a clock like device. There are clocks based on genetic circuits, which produce stable oscillations. Examples include the circadian clock, cell division, menstrual cycle etc. 

Developmental events involve checkpoints and the timing is regulated by several factors such as number of cells, concentration of some protein etc. However, I haven't come across a master clock that integrates and synchronizes all these signals for precise developmental timing. That makes it an interesting area of research.