Yesterday.

tj

I'm dubious it will survive whatever you do. It looks as if the upward growing shoot has died off.

I read to pot in soil when it sprouts, which is why I haven’t. Should I still wait, or should I pot in soil now?

It's hard to see from the pictures but I suspect the sprout has aborted and will never grow. There appear to be two necrotic sprouts. I doubt it'll try again a third time. But there's no harm in potting it up. Nothing to lose.

Thank you

Should have been planted in soil to begin with.

If you do try again, use a largish pot, avocados do NOT transplant well, just be careful about watering . DO NOT bury the seed, leave at least 1/3 above soil level, the SUN and heat will help germination.

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Hmm… everything I read says to put it in water until roots and sprout then plant in soil.

Put it on the ground outside. It will sprout without the pit turning black.

Just plant it now. It will grow. Those sprouts look OK to me. But a close up pic would help. The seed just has some of the papery membrane left on it. That is what is turning black.