There is no time limit for completion - there is a statement which says that 'normally' the induction year is completed within 5 years but you do not lose QTS if you fail to complete within 5 years. As an example, if you had a job that was just 1 day a week it would take 5 years (if you did no other teaching) to complete induction on a part time basis. The more likely scenario is that you have posts that are for more than one day per week which last for at least a term and so you would complete in less than 5 years. BUT you could have a break between posts and that could take you over the 5 years. It would not invalidate your induction or QTS.
I am a PGCE student filled with doubt as to whether teaching is for me. I am not enjoying the daily struggle with the pupils who do not want to learn languages. Anyway, my immediate plan is to stop after June when I complete my PGCE, I doubt I will be looking for a teaching post for next year. If I happen to change my mind in the future and decide to get a job, is there a time limit to do my NQT year? Will my PGCE expire?