When should I start arranging school experience for a primary PGCE?

I have to book two weeks experience in a primary school with the ages I want to teach in the future and five days observing a different age group like secondary or nursery age.

it'd be ideal if you have the experience before applying, it should tell you on the universities websites specifically what they want you to have experience wise. I'm moving this to our teacher training section, you'll hopefully get more responses there.