Its pretty different with every woman and every body type. I had some people saying it was noticable on me at around 20w, and sone people who were still precariously asking me if I was pregnant at 30w. I'm average height with a thicker northern european bone and muscle structure, and it felt like it took forever for me to show. My cousin is very tall and skinny with a thin bone structure (she is chinese) and even though she is due almost five weeks after me she had a visible bump long before I did (14/15w)
I didnt start til bout 21 weeks