Geraniums do not tolerate frost
This also means that geraniums cannot tolerate frost. At best, the temperature should not drop below five to ten degrees Celsius during the growing season, because then the plant stops growing until it gets warmer again. An exception is overwintering, where the degrees mentioned are optimal - after all, the plant should not sprout prematurely.
Geraniums Temperature: Frost is particularly harmful at night
However, it does not harm the geraniums if the temperatures briefly fall below five degrees Celsius - provided there is no frost. The plants cannot tolerate night frost in particular, which is why they should not be planted until after the ice saints - when no more cold nights are to be expected.
If the weather is appropriate, ie outside temperatures in the double-digit range, you can put your geraniums on the balcony earlier. But then it makes more sense to bring the plants in overnight.