How Often Should I Water/Feed Seedlings?

Right now I have two big bud seedlings a week and two days old. I'm using root organics soil which I heard has nutes to last a month but after a week and two days there is yellowing and spots on the leaves. I watered them yesterday and the soil is dry the nextday. I'm giving them around 150 ml of water per watering. Questions..how often to water? How often to feed? And should I even befeeding yet?

Whenever the plant needs it. You should never let the soil/mix dry out entirely, and it has to be somewhat moist to even absorb water properly in the first place. How often you water exactly and how much depends on the container size and in general how quickly it is drying out. You can't really make a determination of precisely what volume of water to supply. Water thoroughly, totally saturate the medium, allow run-off to occur - then wait until the containers have dried out for the most part/lightened up considerably.

Don't allow the medium to become completely dried out.

Started the seedlings in the container they will mature in.2.5gal. I figured small plant, small amounts of water... I was watering about,half cup of water. The temp stays around 85-90 degrees. Should I completely saturate all the medium even with such small root system right now?

1/2C is good for seedlings, but when you water when they mature, you want to thoroughly water until water seeps into the catch pan. Then, dont water again until the pot feels light and the soil is barely moist when stick our finger into the soil. Also, water on the rim of the plant, avoiding the stem so as not to induce stem rot.

i usually don't need to water them for about 5 weeks or so....start in a big bucket i do...
feed when they go weird...then earlier next time around

id say no nutes yet

For seedlings I like to start my soil ones in peat pots so when the root tips creep out I transplant them into bigger pots.

For Peat its easy to water, cause the pot gets wet, then when the medium is mostly dry the pot is also dry. Pretty simple, water til peat is staturated, then when dry complete re-water.

For bigger pots, everyone is different, I prefer to leave a 1in. ring between the top of the pot and top of the soil, I then flood the pot up to ring as quick as possible and let it drain down, most even water spread. Now some people will do this til about 15-20% of pot volume is in the catch pan ( which is discarded immediatly btw ) then leave without watering for 2-3 days with my happy frog mix up to 5 days.

I prefer to water more often so I will do 1 or 2 runs, which should cover about double the distance from soil to rim very well but moisten everything aight allowing me to feed / water a tad more often. With this and taller narrower pots is compacting of the lower soil, or because its so far down doesnt dry out as quickly specially with no roots, then you end up with nasty mushy moist almost rotten soil down there which is no bueno.