Seedling End?/Veg Begin?

I started from seed they are in 1.5" pots w/ promix and a little vermiculite(they will be mom's and dad's and I want them to retain water for long periods w/ low amounts of nutes)

When do you consider the plant to have ended is seedling stage and entered it veg stage? Is there a standard?

Thanks everyone and keep growing.

Amendment 20 compliant

I'd say 3 weeks from popping through the soil.

Or when it get its 4th node.

Thanks

I am starting to see stem growth that resembles a plant in the vegetative state and it starts on the forth node, and its been about 3 weeks.