Is it true, that in D/P it takes 24 hours for Pokémon to migrate, but in Pt/HG/SS it's immediately?
No, you can migrate immediately in any game, but it takes 24 hours to migrate again. So you can't migrate until another 24 hours.
How to change your username
How to add a user avatar
Why was my post hidden?
Flags vs Downvotes
Official PokemonDb League
Type a Pokemon name, type, move or ability to see instant results.