I signed up for the late September/October trip but I’m concerned that time of year will be too hot. I’m looking for 60s and 70s. What month would people recommend?
Dedellac, have you done any research? There are many online websites that give Detailed averages for temps, days of precipitation, sunshine etc -- here's one that gives all that & more for key destinations in Mainland/islands. https://weather-and-climate.com/average-monthly-Rainfall-Temperature-Sunshine-in-Greece
It will show you that by late September, temps are practically perfect for you... max in high 70s, min at night in low 60s. And if you wonder why there aren't huge numbers of group tours scheduled on into November -- again.. do some research... This site shows average # of rainy days in November for popular destinations -- Chania Crete has 15, Athens has about 12, so does Nafplio. Do your homework & you'll stick with your choice.
Our Greek friends warned us about rainy November.
We took the Greece tour starting in mid October and everything was perfect weather-wise and otherwise. Few crowds, residents were happy to see us and one unexpected perk, as it was the last tour of the season, our guide had a budget to use up! Because I prefer cooler weather, I think that time of year is ideal.