their are lots of variables (air temp, water temp, stress level of the fish, general health of the fish in question, etc) but the best answer is, "The shorter the length of time you have to keep the bass out of water, the better".
Preperation is SOOO important. I typically have my livewell (a 100qt icebox) ready with an inch of water in the bottom, so when I lay a fish in it, it won't be on a dry surface. I quckly put in a couple more full buckets of freshwater. Now I can take a few minutes to get out my camera, tripod, and scale. Next I take a test shot or two (without the fish) and turn the scale on.
Finally, I pull the fish out for a few photos (mine will take as many shots as I want, consecutively, without having to reset the camera) then, straight back into the live well. Check the photos. If they are not spot on, I make a few minor camera adjustments, and take a few more. If they look good, I pull the fish out, weigh it, and quickly release it.
So, from the time I hook the fish, to the time I release it, it has not been out of the water for a total time of much more than 1 minute.... and that's split into 3 or 4, 20 second intervels.
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Whatever your doing with your fish, if by the time you release it, you have to hold it, and revive it for any length of time, your not doing it right. It's all about preperation, and practice.
Peace,
Fish
PS, The whole operation can be almost as smooth while shore fishing "if" you remember to carry a stringer rope, so you can keep the fish in the water, while you get your camera and scale ready.
PPS, IMPO, tournament caught fish are going to be subjected to a LOT of stress, which could possibly kill them, time out of the water completely asside. No, I'm not anti-tournament, just stating the facts.