Submitting evidence after 28 day PIP MR deadline

Hi there (and happy New Year). I went to see a welfare rights adviser today about my PIP MR and told her that while my GP has said he will write a letter of support, it might not be done by the January 25 deadline the DWP has given me but she said not to worry about it. I'm confused now as when I rang the DWP on December 28 to tell them I wanted to do an MR they said I had a further 28 days to submit evidence. At the time I didn't challenge her as thought it would make me sound as if I was telling her her job but now I'm worrying I've been given the wrong information.