We investigate the feasibility of implementing an allocation rule with a gradual revelation mechanism, where the agents reveal their private information over time (rather than all at once). With independently distributed types, private values, and transferable utilities satisfying a single crossing property, an ex-post monotonicity condition is sufficient for budget-balanced implementation of any incentive compatible allocation rule with any gradual revelation scheme. When we extend the single crossing property over the set of randomized allocations, a weaker monotonicity condition is both necessary and sufficient for budget-balanced implementation by gradual revelation.