At the end of the day it will be the plant (and environment she lives in) who determines which ions will be uptaken. Since there is actually no reasonable way how to find it out, because they can not speak and you do not have the lab to do the tests, you have to admit, that the best treatment is to provide balanced nutrient solution at right pH the most frequently you are possible, without drowning the roots. So it is actually proven that something between 3-4 hours between events wont cause your roots to rot. There are many more variables which comes to game like calcium carbonate content in your source water, salts you use or was used to mix botlle fert, their nitrate/amonium/urea ratios and content, your pH down, if you use silicates, how strong your food is and environmental factors. In short you want to reset cocos pH and EC values as much as possible since you do not know what is happening there. Have fun with your optimalization