These terms give a loose understanding of development. There's no real way to say this is vege, this is not... except when you flip the light schedule, then you can assume the hormonal trigger in the plant is functional and it is in flower phase without seeing any change in teh plant -- our eyes are not reliable for such things.
So.. when they can handle all the light you can five, that's what matters. This is an evolving thing. You may need to ramp up over several days or maybe they scream for intense light earlier.
The resulting growth pattern is your guide. Too much strethc, give more light. too little stretch with growth nodes that have no internode length between need less light. Take some notes... pre-empt any stretch next time. Make it a well-planned out process based on past experiences.
Everyone's local environmental variables are a bit different, so there is variance between what i do and what you need to do. Trial and error... all you got.
You are in soilless and if you feed around 1.3-1.5 EC well-balanced diet, you can start feeding by the 2nd irrigation if you want to. it will only speed up the process. I stick to 1EC or less for initial charge of my soilless substrate. 2nd irrigation i feed normally and with 10% runoff waste water is probably up to that 1.3EC range immediately, but a little ramp up is fine too.
seeds 'can' power their own growth for 7-10+ days, but a charge in your soilless medium is fine and will have a positive effect. Or, you can wait for ahint of yellow on your cotyledons then fertigate.
fertigate every time with 10% runoff., that's how you use soilless medium. it's providing a consistent level of nutes at all times for the roots to take in. the 10% runoff mitigates a small amount of evaporation that occurs between irrigations and any potential buildup in medium. If you see a tox over time, it means the formula needs to be adjsuted down one way or another. Wont see it next time if you do.