<hr /><i>drh added on 2010-11-01 23:08:10:</i><br />
You can, if you want, go up to the URL bar and append

   <tt>?c=1970-01-01</tt>

(or some other date) to the end of the URL, if you like.  
That is what I normally do.  I will
admit that this is not as nice as having any entry box, but I'm still
struggling to figure out where to put that entry box (without unnecessarily
cluttering the screen).