I think the best data we have so far of the Time & Temperature required for the efficient Decarboxylation of THC is from the GW Pharma patent application:
I graphed these and found best-fit curves in Excel. This is not rigorous, rather a rule of thumb sort of analysis.
The first 2 charts are
THC Decarboxylation vs Heating Time for various Temperatures,and
THC Decarboxylation vs Temperature for various Heating Times
Several conclusions can be drawn.
If you have good temperature control and want the most forgiving time window (for instance to allow time for sample to come up to temperature), you would choose 2.5 hours at 221° F.
If you have good time control but want the most forgiving temperature window (for instance with an imprecise oven thermostat), you would choose 260° F for 0.5 hours.
The best yield is found at 221° F for 2 hours. This may trend higher (speculating on extrapolation) if a slightly lower temperature is chosen. For example, 212° F for 2 hours may have good yield, as well as an being an easy temperature to control.
Good yields are also indicated for 260° F at 0.5 hours. Extrapolation indicates that excellent yields may also be seen at temperatures between 248-284° F for 0.25 hours.
These charts show some similarities to the widely circulated 1990 Journal of Chromatography
And a couple of other views of the same data as above:
In light of all this, I have been getting excellent results by Decarboxylating and Infusing in one step. Oil, cannabis, and lecithin go into a boiling bag at 212° F for 2 hours, agitating frequently.
Does anybody else have hard data, or reproducible results to add?