What’s wrong with my lemon cucumber seedlings?

[Kelsymb]

My cucumbers looked fine yesterday, I watered them in the afternoon and they spent the night outside. I watered from the bottom and they had soaked up most of the water so I left them in the tray overnight. Are they overwatered? I was told to pinch off those brown new leaves coming in and now I feel like I made a mistake, any advice?

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[LastBlow]

You have posted this in march... Cold burn? The tender leaves in the center are the most sensitive to temperature changes. Any update as to how the plants did from then on, please?