The most recommended Black Radish seeding time

In my first post I mentioned that last year I seeded on June 2. This year I seeded on June 30 that is almost the same day especially if you take in consideration that it is a leap year and, due to added day in February, summer solstice came one day early. From Internet I found that the end of June is the most recommended time for seeding in our latitude (53). recently I've got two packages of Black Radish from Russia. One of those is very specific about seeding time - June -25- July 5.

When I asked my Russian friend to find me a few seeds of famous Russian variety Graivoronskaya, (ГРАЙВОРОНСКАЯ)that many gardeners like so much overhere, she told me that in Russia Black Radish is seeded at the day of the Feast of Saints Peter and Paul. In Russia it is July 12 as the Russian Orthodox church is on Julian calendar but for other living on Gregorian calendar it is June 29. I don't know when such tradition get established and should I trust it or not. If it goes back to the time when Black Radish arrived to Russia we have to turn clock back about 6 days for sure to match the sun position for that day. The most important message for me that in Russian the Feast of Saints Peter and Paul closely associated with summer arrival - the time when nights get warm. For me it means there is no more cold nights to trigger vernalization (less changes for bolting) and it is time to seed Black Radish. Feeling a warm of summer in my garden, I seeded black radish and next day we had a garden party for the first time in the season .