I am not arguing with ravshalom above
Just rewording it since it is not quite accurate. (though in practice the outcome is the same).
For counting the days of the tekufa we dont count “meis leis” and even if davening maariv before 1440 hours (60 x 24) after the tekufa, vesein tal umatar is still recited
“Therefore, 60 days from the tekufa is always December 4th, at either 3:00 am, 9:00 am, 3:00 pm, or 9:00 pm, respectively. But since the Jewish day starts in the evening, December 4th at 9:00 pm is considered the following day, December 5th.”
For counting Sixty days the time doesnt matter. 60 days after October 7th is December 5th regardless of what time the Tekufa took place. Thus on most years at the start of “halachic Dec 5th” i.e. after sunset on Dec 4th we start saying vesein tal umatar on day # 60.
EXCEPT that the year before a leap year (is civil years 2011,2015, 2019) when the tekufa is on OCtober 7th at 9:00 PM this is “halachic October 8th” So the tekufa does not occur on October 7th in those years, halachicly it is October 8th (though your calendar still says October 7th for 3 more hours). Sixty days after October 8th is December 6th, after sunset on Dec 5th (even before 9:00 PM) we say vesein tal umatar.
(interestingly, Once in 28 years evening of December 5th is Friday night the year before a leap year and we satrt saying it on the 6th)