sleep does not work in an unscheduled environment, and triggers, waypoints etc are all unscheduled
Try this, this should do the trick
Code:
_heloWp setWaypointStatements ["true", "hint ""hmmmm""; {this spawn {unAssignVehicle _x; _x action [""eject"", vehicle _x]; sleep 0.5;} forEach crew vehicle _this;"}];
Try this, this should do the trick