Shipment.cs

public class Shipment
{
    public int ShipmentId { get; set; }
    public List<Stop> Stops { get; set; }

    public Stop GetStop(int stopId)
    {
        return Stops.Single(x => x.StopId == stopId);
    }

    public List<Stop> GetAllStops()
    {
        return Stops;
    }
}

public class Stop
{
    public int ShipmentId { get; set; }
    public int StopId { get; set; }
    public StopStatus Status { get; set; } = StopStatus.InTransit;
    public DateTime Arrived { get; set; }
    public DateTime? Departed { get; set; }

    public void SetStatus(StopStatus status)
    {
        Status = status;
    }

    public void SetArrivedDateTime(DateTime dateTime)
    {
        Arrived = dateTime;
    }

    public void SetDepartedDateTime(DateTime dateTime)
    {
        Departed = dateTime;
    }
}

public enum StopStatus
{
    InTransit,
    Arrived,
    Departed
}