I was told (by BFG tech) to do a medium length burnout and then let the tires completely cool. This helps get rid of the mold release agent and the heat helps finish the curing process.
For me, the only place I could safely do a burnout was at the track. Even then, I still made my normal passes that day without completely cooling the tire down.
For burnouts, I get the tires spinning in 2nd gear (th400), then go directly to high gear at 6000 rpm, then count to 3 to 5 depending on the tract surface temp. The warmer the track surface, the shorter the burnout needed. The cooler the track, the longer burnout needed. Even then, I don't think you need to do anything longer than 5 seconds or your simply wasting rubber.
After the burnout count is done, I release the line lock and power out to the start line and stage.