Didn't you already ask this, like yesterday or the day before??
This is all you need.....
No, there's nothing like what you're looking for. Because really every beer is different, every temp is different, every yeast is different, different proteins affect yeast differently....there's just way too many different variables involved in the process to be able to give you what you're hoping for.
It's all a generalization just based on what we've observed...but precise and measurable in this regard, can't really be done...
The 3 weeks at 70 degrees, that we recommend tends to be the minimum time it takes for average gravity beers to carbonate and condition. Higher grav beers take longer. Temp and gravity are the two factors that contribute to the time it takes to carb beer.
Using the 3 weeks at 70 as the "mean" an average grav beer at a temp below 70 may take a little longer than one above. Consequently, an average beer beer significantly above 70 may take less time to carb up. (I say may, because there is still a process that the beer has to go through to produce enough gas to carbonate the beer, and that takes time to generate no matter what temp it is at.)
68 is relative close to 70, so 3 weeks is still the rule of thumb.....but if the same beer was at 65 degrees, though not a lot of temp range to us, may indeed be enough to add a week to the carb/conditioning cycle.
In some beers, but maybe not for others....
It's pretty imprecise, every beer/yeast combo is different (we're dealing with living micro-organisms afterall and there always is a wild card factor) but the 3 weeks at 70 tends to be a nice "rule of thumb" to go by for beers in the 1.050 range or below.
(Some folks says add another week for every 10 grav points til you get into higher grav beers (Barleywines/Belgians,) then think in terms of months instead.
What folks seem to forget is that when you stick the beer in the bottles, you are sticking them into separate little fermenters.
Each one is it's own little microcosm, a tiny difference in temps between bottles in storage can affect the yeasties, speed them up or slow them down. Like if you store them in a closet against a warm wall, the beers closest to the heat source may be a tad warmer than those further way, so thy may carb/condition at slightly different rates. I usually store a batch in 2 seperate locations in my loft 1 case in my bedroom which is a little warmer, and the other in the closet in the lving room, which being in a larger space is a tad cooler, at least according to the thermostat next to that closet. It can be 5-10 degrees warmer in my bedroom. So I usually start with that case at three weeks. Giving the other half a little more time.
You can split a batch in half put them in 2 identical carboys, and pitch equal amounts of yeast from the same starter...and have them act completely differently...for some reason on a subatomic level...think about it...yeasties are small...1 degree difference in temp to us, could be a 50 degree difference to them...one fermenter can be a couple degrees warmer because it's closer to a vent all the way across the room and the yeasties take off...
Someone, Grinder I think posted a pic once of 2 carboys touching each other, and one one of the carboys the krausen had formed only on the side that touched the other carboy...probably reacting to the heat of the first fermentation....but it was like symbiotic or something...
With living micro-organisms there is always a wildcard factor in play. Two complete fermentations (and bottle conditioning is just another fermentation) can behave differently due to even the slightest change in enviorment, especially temps.
I don't touch my first beer til it's been 3 weeks in the bottle, then I chill one or 2 for a day or so, and try then.....if they're not carbed or conditioned, I wait another week or two and try again. If you have a pipeline, you may not even get around to a batch until it's ready....