Approximately 1.6-3.8 million sport and recreation concussions occur annually. Yet, there is currently no universal agreement on when an athlete should be permitted to unrestricted play after being diagnosed with a concussion. Simulation-optimization provides a tractable method to optimize the length of the symptom-free waiting period (SFWP), i.e., the number of consecutive days after starting the return-to-play protocol that an athlete must be symptom-free before they are permitted to unrestricted play. We develop a two-part treatment initiation/cessation simulation model consisting of a (1) Controlled Hidden Markov Model [pre-return-to-play] and (2) Uncontrolled Markov Chain [post-return-to-play] and apply four simulation-optimization methods (Crude Monte Carlo, 2-Stage Decomposition, NSGS, KN) to optimize the SFWP. For collegiate men's football and women's soccer, we find an optimal SFWP of approximately 2 and 3.5 weeks, respectively. This research provides clinical decision-support for return-to-play decisions.