Two of the bigger seedlings are dividing and spitting out 3 new sets of leaves instead of just one! That happened much earlier than I expected.
I managed to keep the temperature at around 5° C on my closed balcony during frosty nights by preventing draft and moving the greenhouse frame further away from the glass panels. Unless the temperature drops dramatically, they will be able to handle being outside all winter.
Luckily, the Danish winter is more wet than cold.