a story to supplement what choirfiend said:
this man who was a catechumen while i was one also, he had become a catechumen way before me, and had gone through the inquirer classes in the round prior to mine (i.e. the year before), but after finishing the classes still felt he was not ready to join the Church fully, and so simply attended services and continued to discern for himself for what was probably about an additional year....my priest told me when i became a catechumen that after that step, he does not pressure the catechumen, but simply guides and is present to answer questions, etc., and that it would be up to the catechumen to speak up about feeling ready, at which time my priest would either concur or suggest more time...so this man i mentioned was received into the church only a week prior to me, but had probably been a catechumen twice as long. it really is a case by case basis.