gistfile1.cs

// started here
public class Entry : Entity
{
  private DateTime _createdAt;
  
  public bool IsWithinEditWindow()
  {
    return _createdAt.IsAfter(20.Minutes().Ago());
  }
}

// moving toward configurable
public class Entry : Entity
{
  private DateTime _createdAt;
  private static TimeSpan _editTimeWindow = 20.Minutes();
  
  public bool IsWithinEditWindow()
  {
    return _createdAt.IsAfter(_editTimeWindow.Ago());
  }
}

// configurable via outside definition
public class Entry : Entity
{
  private DateTime _createdAt;
  
  // is a static gateway the best we can do here?
  private static TimeSpan _editTimeWindow = SomeConfigThing.EntryEditTimeWindow ?? 20.Minutes();
  
  public bool IsWithinEditWindow()
  {
    return _createdAt.IsAfter(_editTimeWindow.Ago());
  }
}