I'm not aware that this cactus is self-fertile. I have a Gymnocalycium mihanovichii var. friedrichii myself and after several blooms this year outdoors, nothing (my avatar picture is of my Gymnocalycium mihanovichii var. friedrichii in bloom).
As to why the flower closed so soon, I think it only lasts a day (if I remember correctly... my cacti are spending the summer at my Mom's).
If what I read was correct, it is a "rare sight" to see one of the grafted ones bloom. And it's possible it has opened already, the grafted ones' flowers are not all that spectacular. They're not nearly as large as the other Gymnocalycium's flowers.
Planto
