This research used an optimization method to highlight the importance of time scales in the design of a bottom-fixed OWC (oscillating water column). The different time scales studied were a sea state, a season, and a year. For the last two scales, a stochastic formulation was used to take into account the random nature of the wave climate in the time interval considered. This paper also describes a general methodology for the study of the non-stationary performance of an OWC device during its useful life, which was applied to obtain the available pneumatic power. It entailed simulations of the wave climate and the corresponding OWC-related performance magnitude, which reproduced the intra-annual and interannual climate variability at the site. This methodology was used to analyze the management-related random variables for three optimal OWC configurations on different time scales. The results of this study show that OWC performance can be enhanced by designing systems whose configuration can be adapted to successive sea states. This opens a line of research with promising technological implications that is well worth exploring in greater depth.