I'm glad you're really enjoying it.

It may not be the author's place to say it, but I'm pretty sure this is the most detailed blood mod you'll find out there.
The oxidizing effect does occur over a fairly long period by Doom standards, which is about 5 minutes or so. There is no such effect for blue or green blood, but I may add that later. The reason the blood which is more misted onto the walls does not oxidize is that it is a replacement of ZDoom's standard BloodSplatter, which means if I make it change colors to, say, a dark reddish-brown, then it will do that also for blue and green bloods, resulting in no difference between any of them after 5 minutes. Since they all turned the same color, I decided to just neglect the feature. I do not think there is anyway for me to circumvent it, but if anyone knows of a way, I'm open to suggestions.
I am baffled by the fact that there is, indeed, far less runny blood for red blood than there is for green or blue. The green and blue implementations are based on the red one. The code is identical as far as I know. But I have noticed this from day one myself, that the red blood does not behave as I have prescribed. I'll take another look at it just to make sure I didn't make some kind of blatant error, but it seems to be something on ZDoom's end.
As far as making a slider for the time it takes wall blood to oxidize, I dunno. I'm more worried about the impact the fog effects might have on slower machines; that's a lot of overlapping transparency to render. I'd like to make the Blood Lifespan slider affect blood fog in water; I don't think it's possible for me to change the oxidizing effect for wall blood; it'll just have to remain some constant value. I might reduce it to 2 minutes, though. I can't have it happening too quickly, or the player could sit and watch the blood dry, which doesn't feel incredibly realistic. It needs to be subtle.
Ceiling and floor blood does not oxidize. This would require doubling the number of blood actors in the game, which would produce quite the performance impact in many situations (especially on moving platforms).