This will depend on exact circumstances, but put like that plants will grow
as much in a day no matter how long it lasts (24 hours or a month)

Yes, but. It depends on the plant's metabolism, doesn't it? Many of my orchids
are CAM (I know, we lost the original questioner by now). I have my lights on
18 hours a day. When I went to 19 hours, my Cattleyas exhibited black shoots,
which for them is a sign of sleep deprivation. It's been 18 hours ever since. I
am not about to experiment with lengthening the night period at the same time.
It wouldn't buy the result I'm looking for anyway, which is maximum total light
exposure.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)