This mod is entirely based on (and simple edit of) the following old 2016 mod:

"Vault 81 - Timed Mole Rat Disease (60 minutes)"
https://www.nexusmods.com/fallout4/mods/15012

The author of that mod, Spherikal, stated full permission to do whatever - so credit to them.
What I did was work out the timing they used to make it 60 minutes and then multiply it into weeks.
I also added an esl-flag which was absent in the orignal mod at my time of editing - and prob not a thing in 2016.

As I don't have a save-game file from just before Vault 81 I'm just assuming the original mod works - it's just a simple single stat change anyway. But if you're about to get infected, I'll welcome feedback.

Game logic and mod rationale:
Whilst a vault-dweller, especially a young kid, might not have enough immunity, the Sole Survivor is at peak adult age/condition and from a different, much healthier/robost above-ground era. Still, this is a nasty disease, one that takes a month or two for our hero to eventually get over. This means you suffer enough but not for so long that the pill-icon (and minor loss of HP) forever annoys you. And in any case here's a fun fact: whilst the disease is supposedly "permanent" without a cure, the actual in-game preset is roughly 2.5 years - so, no, it ain't permanent!

I've provided 4 versions - 4, 6, 8 and 10 weeks (if my maths is correct). And esl-flagged them. ONLY INSTALL ONE! And please note these timings might not be exact (and maybe affected by unlocked FPS if timer-count is based on 60 FPS). 

How about shorter? And/or esl-flag the original? Or...?
No to all. If you want shorter just use the original mod and sleep it off for a number of days. And as the original author already very kindly gives permission, I feel doing shorter or esl-flagging theirs is stepping on toes too much. There's already other esl/flagged molerat cures - and anyway the whole purpose of my offering is to make you suffer for an extended time!

Installation:
Best install at any time before going down into Vault 81 for the first time - or at least before starting the quest down there called "Hole in the Wall". I've no idea if it might work if installing after getting infected.

Compatibility and Load Order:
Doesn't conflict with UFO4P (at least not the v2.1.3 I'm still using). Might conflict with any other molerat disease mod or any game-balancing mod which might make changes to molerat disease so load after them, otherwise load anywhere (so you might as well stick it in somewhere early).

Permissions:
I can hardly restrict an edit of another freely given mod - credit Spherikal and mention little old me, Streetyson.