Before revision:  Such timer mechanisms are difficult to implement at the level of single cells , however, due to saturation in molecular components and stochasticity in the limited intracellular space.
After revision:  At the single-cell level, timer mechanisms can be implemented with genetic circuits: sets of genes connected to achieve specific tasks. However, such systems are difficult to implement at the level of single cells , however, due to saturation in molecular components and stochasticity in the limited intracellular space.