.....
ActionsJournal actionsJournalEntry =
 TestFactory.CreateActionEntry(.....);

if (/* some condition */)
{
  actionsJournalEntry.CreatedDate = DateTime.Now.AddDay(30); // else it will be null
}

ent.ActionsJournals.AddObject(actionsJournalEntry);

ent.SaveChanges();
....

public partial class ActionsJournal
{
    public class ActionsJournal() {
        CreatedDate = DateTime.Now.AddDay(30);
    }
}