If you are taking a while to do photos and its quite a few fish, have an airstone ready to pop in the bucket. Amazing how many times a phone can ring or you get visitors or a kid wants you when setting up to do pleco pics.
I especially bought a little betta fish tank for photos. Its small, you can cover the top from light and give them a few minutes and they will lose their stress colors for better photos.
Try balancing the edge of the betta tank over another tank and take vent shots from under.
Breaks your knees and back trying to focus it but is doable for just a few fish.
For a vent shot with it all hanging out and not sucked in, I handle for out of water shots but its rather a gentle lift them out in your hand (they will put out their prongs for you so you aren't damaging slime coat) and carefully hold with thumb over mouth (they seem ok with that) and index and middle finger either side of the dorsal fin. Its gentle hold, so as not to damage slime coat and they dont seem to struggle at all in that position.
Advisable to have your camera on and pre-focussed to the exact distance you wish to take the photo too. This is only a few seconds out of water.
For getting an erect tail fin, the held position is good as well. Paricularly if you are making sure your fish has a L333 tail and is not a L066 with a forked tail mascarading as a L333 in your tank.
As to time they 'can' spend out of water? As long as they are moist and don't dry out, hours.
I've had fry drop off wood into a tiny drop of water on the floor and found it fine an hour later, ooops.