This weekend minimum, next week tops. Mark your calendars.That is completely unreasonable thinking. Adding support for a specific firmware version, working backwards, would most likely entail finding if the vulnerability existed in said prior version and if so could it be exploited in the same fashion as done in 9.X where it was first noticed. It is entirely possible the exploit could have relied on code not introduced until 9.0 and not have be usable in a prior version at all. It's also possible that the exploitable code could have existed all along since 1.0 and the method used to exploit it not been possible until yet further code was introduced in later firmwares. Basically - anything's possible but the probability that the exact same amount of time is needed to get the exploit working on each and every firmware is VERY slim.
In other words, while your math isn't flawed, the logic behind it is...
(but I still hope you're right because my XL is waiting! )
Edit: Considering GWs update news policy, they'd either update us to say how long itd take, or how close they are to being done.