[bower]

There is a big difference in varieties which are cold tolerant. All the tomatoes I regularly grow will set and grow fruit with night temps of 50 F, as long as day temperature gets to 60 F. Any tomatoes which you know are as cold tolerant as Stupice or Moravsky Div should not need two nights of 55 F to make fruit.
I will just check my data, Vladimir, to see when in the season we have two nights of 55F, because I think by then I usually have a lot of fruit set.


Well, I looked at the data from 4 different years and I can't find any fruit set where there wasn't two nights of 55 F in the time between flower open and set. Bearing in mind it can take anywhere from 8 days and up (typically 15 days but longer in cooler weather) from the time flower opens to the time fruit sets, there were colder nights, even mostly colder nights in the early ones but there were at least two days of 55+ nights in every interval.

So it looks like Florida U conclusion is correct.