Dreaded brown envelope

Although i recently won my appeal for DLA that dated back over a year ago, my renewal form came through the post Monday as the DLA had a limitation only until September 2012. I've picked it up and looked at it several times and so far have only filled in my name & address...
Question is how long to do have to fill it in & send it back as at the moment i'm not in a good place and struggling to fill it in? Will they contact my doctor or consultant for a medical report before or after the form as been returned?

Thank you Gordon, mid june should give me time to fill it out then? As for them contacting my doctor or consultant for their report will want to obtain it before or after they have received the claim pack? As obviously i need to speak to my GP/Consultant to warn them. Unfortunately last time my gp sent a report he didn't give an accurate one which resulted in me appealing in the first place!

Sorry can i also ask another question? Is it possible to make sure the DWP get reports from BOTH GP & Consultant. This is because my consultant would be better to explain the physical side of my illness (Chronic Migraine/Occipital Neuralgia) as this is his speciality & my GP would be better to explain the depression as i see him quite regular!

Meh... When i requested a report last time for my appeal my consultant was very happy to provide me with support but is a stickler for paperwork. He would only provide information if he received the correct paperwork (i.e the official form the DWP use) as he said it was against the patient confidentiality act?! This time round i'm know he would provide that inform provided it gets a form! Is it possible to get a copy of that form so that i can give it to him myself? Hope this makes sense?