Stop.cs

public class PickupStop : Stop
{
    public PickupStop(int stopId, Address address, DateTime scheduled)
        : base(stopId, address, scheduled)
    {
        StopId = stopId;
        Address = address;
    }
}

public class DeliveryStop : Stop
{
    public DeliveryStop(int stopId, Address address, DateTime scheduled)
        : base(stopId, address, scheduled)
    {
        StopId = stopId;
        Address = address;
    }
}

public abstract class Stop
{
    public int StopId { get; protected set; }
    public StopStatus Status { get; private set; } = StopStatus.InTransit;
    public Address Address { get; protected set;}
    public DateTime Scheduled { get; }
    public DateTime? Departed { get;  protected set; }

    public Stop(int stopId, Address address, DateTime scheduled)
    {
        StopId = stopId;
        Address = address;
        Scheduled = scheduled;
    }

    public void Arrive()
    {
        if (Status != StopStatus.InTransit)
        {
            throw new InvalidOperationException("Stop has already arrived.");
        }

        Status = StopStatus.Arrived;
    }

    public void Depart()
    {
        if (Status == StopStatus.Departed)
        {
            throw new InvalidOperationException("Stop has already departed.");
        }

        if (Status == StopStatus.InTransit)
        {
            throw new InvalidOperationException("Stop hasn't arrived yet.");
        }

        Status = StopStatus.Departed;
        Departed = DateTime.UtcNow;
    }
}

public enum StopStatus
{
    InTransit,
    Arrived,
    Departed
}