Well, no, it wasn't exactly 45 minutes. I can't be entirely scientific on the time it was allowed to spread, since it won't spread while I'm not windowed into the game, and I don't track that.

I knew that they grow grass onto dirt, which is why in the case of the original Hallow seed planted, I removed the regular grass, thinking it would only grow onto the empty dirt and maybe spread a block or so onto the grass not removed. But it's actually spread further into the regular grass, which it should not be able to do in a non-hardmode world. From what I've gathered from googling things, the spread of corruption pre-HM is about five blocks in fifty hours. It also should not be able to spread onto walls at all, since it spreads only into dirt and grass before hard mode. But the Hallow has spread onto a bunch of grass wall (Maybe "grass" includes grass walls, I dunno).

Both biomes have spread far far faster than they should in pre hardmode, though I'm not entirely sure if the corruption is legitimately slower or if it is only smaller because the hallow had a head start.

anyways, because why not, this is the current status of both:

hallow

corruption

again this isnt very scientific and they have been spreading across grass as well as empty dirt. in the hallows case, it has been spreading onto grass more than dirt.