The light duration is also affected/determined by the intensity (PPFD). It's another part of that equation that can be adjusted. (
Edit: By the way, what I was meaning say here was DLI: intensity and duration equating to DLI/daily lighting integral, and how we can adjust the first two while keeping the DLI the same, if we need to. That's all.) And some do 24/0 for veg due to temp/rh stability needs, like samwell said.
VPD requires that third variable of plant temp (lst). It can be very misleading without knowing that part.
Edit: not "correcting" anyone, just trying to add to discussion.
Anyway, good luck
@FlowerPower88. I didn't see what kinda light you're using. If you can afford one, get an ir thermometer "gun", they're not expensive.