How fast does Corruption/Crimson spread?

It'll spread for the most part about 3-6 blocks per day depending on your biome and blocks. And to be honest after Hardmode is initiated you don't NEED the crimson really. So go buy the clentaminator and just ... well, get rid of it. If you ever need more just buy red solution from Steampunker during blood moon and make some :) Solves the pesky hardmode spred problem. Quite often a good idea is to make a world that is 100% crimson/corruption and have my home world corruption/crimson free! If you REALLY aren't capable of killing the WoF in a day or so (irl) then a good idea is to make a 3 block wide helevator on either side of corruption/crimson so that it can't spread! Hope this helped :)

Itll spread about 3-6 blocks per day. The blocks it spreads on are: Grass Stone Mud Sand. a way to stop the spread is to put a 3 block thick wood wall around the whole corruption biome than put a door on the top. The dryad also sells purification powder which gets rid of corruption and crimson.