On what day

It depends... some soil will keep a plant happy for 2+ months... Where as in soilless, you are fertilizing from the get-go 100% of needs. If in soil, wait to see some deficiencies before ramping up - and when you do rampe up start with a lower dose than instructed. Take notes. If you use the same soil and fertilizer in next cycle, you can form a better plan to avoid symptoms... too many variables for a one-size-fits-all recommendation. you need to learn how to ride that bike.. when to supplement various bits of nutrients andn when to start providing a wider spectrum of nutrients at higher concentrations over time. If in soilless, like coco, you'll want a well-balanced 1.3-1.5EC (does not count tap water EC) diet from the start with every irrigation and religiously get 10% runoff waste to avoid buildup. easy-peasy. basic rules -- 1) fully saturate 2) wait for appropriate dryback and repeat. Soilless context also needs the 10% runoff. If doing these basic things ever causes a problem you are either watering too soon or have a poorly constituted soil - add more perlite or similar. Also, you never choose the volume to give. you use the volume of water necessary to complete the task as stated.

Soil with nutrient 2-3 weeks after. Soil without straight away

when it needs to... how we'd know ? There is no dairy or pics or any information... the dumb question leads to equal answer... duh.

Hey it depends by the soil you have. If it's a soiless medium ( like Coco), you have to feed immediately. If it's light mix you can start feeding after 2 weeks