When is the right time to add salt and sugar to our babies' food? And if we can already, is there a specific quantity per dish/day?

Don't spoil her taste bud with salt or sugar. Try other food types. Cook porridge with pork n pumpkin but take away the pork before serving. The sweetness of the pork gets into the porridge plus the pumpkin too. I would only intro after age 2 - both salt and soya sauce