It takes 16 hours for an Oran Berry tree to fully grow. Use the 'Berry Pots' item to grow berries. (available from the Goldenrod flower shop, after the sudowoodo incident)
Here are some other places where you can find Oran Berries:
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In HG/SS you trade Shards for Berries. Trade with Jugglers in Violet City and Fuchsia City.
no
There are no PokeBlocks in HG/SS.
You cannot trade a Pokemon from the 5th generation to the 4th generation or below. Getting Pokemon from Black/White to HG/SS is impossible. You can migrate Pokemon from HG/SS to Black/White though.
I was told he's only in platinum, HG, and SS.