Oscillations underlie the fundamental process of cell proliferation, driving cell doubling. These oscillations are controlled by checkpoint systems that surveil the cell for errors such as DNA damage and activate error-correction mechanisms. Checkpoints are often thought to be simple: activating in the presence of errors and off otherwise. However, in an increasing number of systems it is actually observed that when errors are not fixed, checkpoints turn off regardless after some time. We asked whether cellular error correction systems reflect the timescales of oscillations. That is, are error correction systems shaped by time pressure on cells to divide and proliferate? We have also been leveraging the rhythms of cellular doubling for engineering. In particular, we realized that the need for certain proteins to cycle during cellular replication can be used to evolve proteins that switch between different states. I will present this new approach to "directed evolution", which we have applied to light-sensitive proteins and logic gates.