Sleep is important! That said, I do a lot of coding late at night anyway. This is mostly because I have a five month old at home who takes up all of my extra time while he's awake. Then I'm cleaning up, making bottles, etc. Finally around 10 or 11, everyone's in bed and I have some time to myself, so I go and code.
I know I shouldn't keep doing that indefinitely, though, or it might catch up with me in a bad way.
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