pip review

hi i got my pip review through on the 26 oct 19 it states must be sent back by 18 nov 19 that only leaves me 20 days to get it done and posted back to them.This is to much pressure will it go against me if i ask for more time.I have stage 4 C.o.P.D that is about the same as when i was rewarded pip two years ago .The only change since is i now have sciatica and lower back pain often felt after coughing .This is my first pip review and need your advice please.