What is the typical touchdown angle of a large airliner?
(Source: 744 FCTM)

The relevant text reads:


  Airplane body attitudes are based upon typical landing weights, flaps 30,
  VREF 30 + 5 (approach) and VREF 30 + 0 (landing), and should be
  reduced by 1° for each 5 knots above this speed.
  
  Typical landing flare times range from 4 to 8 seconds and are a function of
  approach speed.
  
  Initiate the flare when the
  main gear is approximately 30 feet above the runway by increasing pitch attitude
  approximately 2° - 3°. This slows the rate of descent.


So for one of the largest, a delta of 2-3° is achieved in 4 to 8 seconds. As the text shows, the attitude varies based on speed, flaps, etc., so we can take the delta as both the optimum and typical value.

I checked the 777-200 FCTM, the values are different. And of course the smaller the plane, say a 737, the later the flare is initiated due to the smaller [and later] the ground effect.