HCV does not lengthen the window period. People on chemo, people taking antirejections drugs for organ transplants and chronic IV drug abusers my take longer than 3 months post exposure but it is rare.
Three month is a gold standard. Six moth if for patient with Hep C or co-infection.
We cannot speak for what other people advise. There are plenty of health care providers who are not properly educated about HIV and the official window periods. We can only tell you what the official guidelines are...3 months.