The Multi-Center Traffic Management Advisor (McTMA) provides a platform for regional or national traffic flow management. It allows long-range, cooperative, time-based metering to constrained resources, such as airports or air route traffic control center boundaries. Part of the demand for resources is composed of proposed departures, whose actual departure time is difficult to predict. For this reason, McTMA does not schedule the departures in advance, but rather relies on traffic managers to input their requested departure time. Because this action occurs only a short time before the aircraft's actual departure, McTMA may be unable to accurately predict the amount of delay airborne aircraft need to accommodate the departures. This study provides a preliminary analysis on the effects proposed departures have on airborne delay for a 400 nautical mile metering horizon. Results indicate that within this range, delays needed by airborne aircraft to accommodate these proposed departures are feasible for controllers to handle. However, McTMA needs to be extended beyond its current metering limits to support traffic flow management nationwide. As the metering horizon increases, the proportion of demand that is comprised of such proposed departures increases. Supporting data shows that a rise in the number of proposed departures worsens the effect on airborne delays.