Any interesting concept, but a bit too incapacitating to be useful in a campaign unless it happens to affect an npc the chars care deeply about and begin a quest to find the cure for.
I like Mourn's idea of the mites making the afflicted move slower, since an infected character woudl still be playable, just under the effect of a permnant "slow" spell.
There is something in particular that bugs me (haha... ha.) Im not sure how the mites work, but I think that might be better explained by why they exist. Is time itself made up of little insects? Are they parasites on time? I'm just having issues wrapping my mind around why they are what they are and why they do what they do.
25-Some gold nuggets
A few nuggets of genuine gold, quarried by slaves in a mountain range long settled by Orcs. No magic, they are what they are and the PCs should be able to turn them into legal money or swap them for something of value with very little trouble.