Watering and Nutes

Let's say I water my plant every 3 days and I give it 1/4 gal. When I give my nutes (in place of a watering), do I give it the same amount as if it were straight water (1/4 gal.)?

yes you just tailor the nutes to how much water is in your container

When do you start adding nutes? at what size, time, etc???

I start when they are 2 weeks old at 1/4 strength.

it all depends on what soil you have. how much nutes is stored in soil as well.i would give them nutes every other watering, some soils are hot to start so no nutes are needed. for 2-3 week mim... every 3 days is good as your plants get bigger you might have to go to every 2 days.