RE it is against an explicit Remah
See OC 117:1
Mechaber says we say it on the 60th day after the Tekufa
The Remah says the day of the tekufa is included.
The Mishna Berura points out that there is always 2 days between the day of the tekufa and the day we say vesein tal umatar. His example is if the Tekufa was Sunday then we start vesein tal umatar at Maariv of yom revviii (Ie Tuesday night). This is not wah twe did according to your incorrect caclulation. Sept 23 was Shabbos, if this was the tekufa we would have started Monday night
Do you not remeber discussing this last year? and the year before? and before?
soem of the comments are in this thread