1.
Occasionally. Usually denotes a relatively short (but
indeterminate) amount of time.
Far off he heard the city's hum and noise,
And now and then the shriller laughter where
The passionate purity of brown-limbed boys
Wrestled or raced in the clear healthful
air... Charmides I. by Oscar Wilde
Now and then a visitor wept, to be sure; but this slaughtering machine ran on, visitors or no visitors. It was like some horrible crime committed in a dungeon, all unseen and unheeded, buried out of sight and of memory... The Jungle, Chapter 3 by Upton Sinclair
2. Used to
juxtapose (or simply qualify the time between) two
distinct time periods. This usage is similar to, but less common than
then and now.
And I am pushing my publishing house... I've got to earn $50,000 for it between now and then--which I will do if
I keep my health. A Letter to Joe T. Goodman from Mark Twain (Samuel Clemens).