Back on topic, I've rarely (uh, never) gotten enough growth in 24 hours from a "fresh" pack on a stir plate or shaker, even when oxygenated right before.
Maybe I don't know what to expect, but the color changing from brown or dark tan to light tan or creamy is my clue (unless it's WLP002/WY1968, which turn into "egg drop soup" when done), and it never happens in that short time period.
Instead, it takes 2-3 days from most fresh packs. I give it the extra 12-24 hours after the color change, for all security. I usually end up with a big yeast cake, about 1/2" in a 1/2 gallon pickle jar or 2 liter flask, about 4 ounces of thick, barely pourable slurry. Occasionally more.
Now most "fresh" WLP or WY I get here (MDHB) is 2-3 months old, but with WhiteLabs' PurePitch packs that should not be a problem, with only 3% viability decrease per month, at least during the first 3-6 months.
Look closely at inoculation rate/starter volume vs. growth on BrewUnited's yeast calc. and see how changing those helps in maximizing growth.
Even with only 50 billion (viable) cells at the onstart (half the settled slurry level in an old WLP yeast tube) you can easily get 300 billion cells in a 1.8 liter starter, when done. But, I doubt that happening within a mere 24 hours, unless that slurry is already active, ready to go, freshly harvested from a previous starter, not cold crashed.
Such as using 200 ml of the previous starter, without crashing and decanting, and adding 1.8 liter of fresh 1.041 wort (yielding effectively 2 liters of 1.037). Something like that.
Over-stirring, past done is not recommended. So letting half of your fresh active vitality starter stir another 3 days with fresh wort may be too long. With a crashed slurry that's no more than a few weeks old, probably perfect.
I need to re-read the yeast book again.