uk family visitor visa 6 months or 180 days

My father has got 6 months family visitor visa from 4 aug to 4 feb on visa page and it says duration of stay is 180 days. if book between 4 aug to 3 feb it comes around just above 180 days. I am wondering which one is correct so i can book my tickets accordingly. i really appreciate your advise. some tickets are cheaper around 3 or 4th feb.

many thanks for your help.

I'd go by the dates listed on the visa.

Me thinks you are reading too much into the "180 days" bit. I would read it as shorthand/approximation for six months, nothing more.