Growing Poppies In Pots Outdoors; What Am I Doing Wrong?

I have planted poppies before with great success however straight into the ground where they had about 4-5hrs of light a day. Now I'm in an apartment with a small balcony where I have about 5-6 pots with poppie seeds and small poppy sprouts.

The problem is once my poppie sprouts grow just a little tall, just enough to have a 2-3cm stem (which is just a tiny white stem, very fragile at this point), then they die off. The thing is we've had extreme heat the past couple days with humidity felt like almost 40C* and im thinking maybe the heat killed them, although they get direct sunlight less than 4hrs a day.

Also I do water them (lightly) at night.

What am I doint wrong, I thought poppies loved a lot of light?

Cheers