I've done it both ways and didn't really see a difference. I wasn't long at 24/0, maybe like 3 days, but either way you should be fine.
I'm doing 18/6 right now.
I guess the only con to leaving the lights on 24/0 would be if heat was an issue and cost of running them.
You will be safe either way you do it....
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Heat isn't an issue for a 18/6 vs 24/0. The temps aren't going to go up that much more that last hours. The heat is already there at about the 5 hour mark.
Let me clarify what I meant. If you are running lights that constantly keep them temps at 84-85, then running them for 24 hours straight would be worse IMO. The temps will settle down when you give them 6 hours of darkness.
But it will hit that 85 degrees LONG before the 18 mark hits.
And if the temp drops from 85 to 70 during dark, thats a large drop.
(if you have high temps, add venting and/or CO2.)