Birchas Hachama is said once every 28 years. According to Wikipedia it is said when the sun has returned to ts original position when the world was created.
Jewish tradition says that when the Sun completes this cycle, it has returned to its position when the world was created.
According to the Rabbi Dovid Heber from the Star-K in the footnotes number 11 this is based on the opinion of Rebbi Yehoshua that the world was created in Nissan.
As far as I know and from the answer here the accepted month of the creation of the world is Tishrei.
I have not found anyone suggesting that we should say Birchas Hachama in Tishrei. Why?