IMO
She became an icon during the True Blue era (even though the LAV performance was already iconic). She became a legend during the COADF era when she was slaying everywhere/Hard Candy era when she was inducted into the Rock & Roll Hall of Fame.
I doubt people can answer Madonna's if you are not a fan because in fact Madonna has 30+ years of fame.
I am a HUGE fan myself but I'm still afraid to answer since I wasn't born in the 80s.
However I do still look up to her a lot but eventually I can't tell.
To me, she's a legend ever since Like A Prayer and an icon ever since Like A Virgin.
Icon: LAV VMA performance.
Legend: Like a Prayer
Queen of Pop: Vogue
Queen of Music/Goddess of Love: Ray of Light
Historical figure level, like Cleopatra or Jesus: Hung Up / Hard Candy Tour