There is no general deadline for starting a PIP claim, but you should contact the DWP as soon as you think you may qualify. Your claim date is usually when you first make contact, and payments are not normally backdated to before that date. After starting a claim, you will usually have one month to return the ‘How your disability affects you’ form, although you can ask the DWP for more time. Check the latest rules on GOV.UK, as Scotland uses Adult Disability Payment instead of PIP.