Outside the while loop create an index variable which starts at 0. Also create another variable which will store a time and set its value to inline]pygame.time.get_ticks()[/inline]. Now in the while loop create an if statement something like this:
timeStamp = pygame.time.get_ticks() if timeStamp - lastTimeStamp >= 500: # lastTimeStamp is the variable storing time and replace 500 with another integer that works well # get the enemy with the number value from the index variable lastTimeStamp = timeStamp # resets the time stamp index += 1 # The index variableI think this will work