Chess move by move

On page 10 of Chess Life,Winter 2004, Bobby Fischer is quoted as saying: "I have played over several hundred of Morphy's games, and am continually surprised and entertained by his ingenuity. It has taken me twenty minutes at times to find the proper response to one of his move."
Why would Fischer spend 20 minutes trying to find a solution to Morphy's move? One reason could be that he needed to know how he would respond if somebody played the Morphy moves (from rote) against him. Second, may be he was trying to beat Morphy! If you are going to be the greatest ever... you have to be able to respond to anything that may be thrown at you, by others, whether they are dead or alive ;-)
20 minutes trying to analyze one move and come up with a response to it! I guess just like life, you get out of Chess what you put in.
How long do you spend analyzing games of the masters? Do you just take their moves as the last word?
So there is a tip: Beat the greatest Masters at their own game!