I don't know how she knows what time it is, but Cleo has a fit every
morning an hour before dawn.  If she happens to be sleeping in the
bedroom with us she wakes us up.  She is determined to be in the
correct window when the first rays of sunshine come streaming in.  The
correct window isn't in the bedroom, and we sleep with the door is
closed.  This quiet cat suddenly turns very vocal and if we ignore her
"let me out now" mews she will resort to walking on us.  If we ignore
that, she sits on one of us and make whining noises.  Arg!  There is
no way to ignore a cat that wants you to get up.

They know what time of the year it is too.  Two weeks before Christmas
Miss Kitty (my former cat) would start waiting at the refrigerator
door and look in it every time we opened it.  It was the only time of
the year she was interested in the contents of the 'fridge.  She was
waiting for the turkey to appear.  :-)
Debra in VA