College admission platforms aim at achieving a balance between avoiding congestion and allowing for ex-post flexibility in students’ matches. The latter is crucial as the existence of off platform options implies that some students will drop out of the platform in favor of their outside option, freeing up seats in on-platform programs. Sequential assignment procedures introduce such flexibility, by creating a dynamic trade-off for students: they can choose to delay their enrollment decision to receive a better offer later, at the cost of waiting before knowing their final admission outcome. We quantify this trade-off in a setting in which waiting costs can be heterogeneous. We use rich administrative data on rank-ordered lists and waiting decisions from the French college admission system to estimate a dynamic model of application and acceptance decisions. We find that waiting costs are large, especially for students of low socio-economic status. Nevertheless, we find large welfare gains for all groups from using a multi-round rather than a more standard single-round system, as it increases the number of matches and enables students to enroll in more specialized programs. enables students to enroll in more specialized programs.