well, certainly there are 2 options here that you can choose at the end, Wilfred.
I hope this thread will not turn into a bashing arena (like Philanddeb predicted), since I think this is a great question that can bring up good discussions. I would like to start with the statement that my post is not meant to be flaming in nature.
As for my advise goes, recently I had a chance to talk in depth with Dr. Frances Baines about the effect of lights to reptile's circadian rhythm.
The gist of the conversation was that reptiles are "wired" in a different way than mammal.
Chameleon, as many other diurnal lizard, recognized the presence of light as the time to wake up.
If we, somehow, manipulate that timing, certainly, it is easy to understand that the impact of continuous exposure can proven to be detrimental to your cham's general health.
This is, imho, more than a matter of "method." This isn't something like the difference between misting twice a day or three times a day.. or the difference between using a hibiscus or Dwarf Umbrella tree..
So, Trevor, I am sure that Dr. Greek will agree with me that turning on uvb light for 24 hours will eventually cause health problem to chameleons.
Take this illustration as an example:
Let say that we put 1 chameleon to the test.
After he get used to the routine of 12 hours lights on and 12 hours lights off,
we disrupt the timing by turning on the lights during his sleeping hours..
I am sure he will wake up during the first week..
Perhaps, after 2 weeks or so of such interruptions, he'll probably will sleep like a log even when we turned on the light.
Now, the question is.. is this what we called adaptation? Not likely.. Adaptation is probably the wrong choice of word.
imho, in this case, we simply put our chameleon to a point where he's too tired to wake up during that midnight interruption.
Now, a long term of inducing such "method" can probably mess with our chameleon's health, don't you think?
Perhaps, a 2 minutes or 5 minutes is not something that we should worry about.. but, in reality, we do not exactly sure that it won't affect his long term health.
When in doubt, it is best to mimic the natural environment of where your chameleon's originated. I think it is safe to say that Madagascar or Yemen never have a moment where the sun suddenly shine at the brightest for a period of time in the middle of the night.
Of course, at the end of the day, we will never know. Unless, if someone here is willing to test one of their chameleon to be subjected to such condition.
My point is why expose our pet to such activity that we might possibly affect his health where we can be the better owner by just working outside the reptile's room or carrying the flash light to move about in that dark room?