If you want to calculate it, every 2 days you get 1 free pull

Every 20 days you get 1 ninja (since 10 pull you most likely get a ninja)

let's say every 120 pull you get 3 susano'o fragment (quoting form veelocity)

so every 240 days you get 3 susano'o

round it to 360 days for 4 susano

80 susano fragment mean... well 20 years of free pulling will net you one, without using any seal scroll of course