Imo i start to count as soon as they break earth. Its really your preference tge first couple weeks of life isnt gonna be any spectacular growth, but as soon as she gets her legs shes off to the races. I dont really mess with breeder duggestions much every plant will tell you what she wants/needs when the time comes, but i get it better to be proactive then reactive.
So lets say you counted since she sprouted. Shes been alive what maybe week week ina half. If your looking to go by a time line, that stems from a suggestion of a breeder. Instead of trying to count the days the plant has been alive, count by what she is doing. What i mean by this is simply wait, once you got her producing knodes at a noticable rate. (I.E. growth every day ) then i would start to count because its then that she will begin to double in size weekly, and all your LST comes into play. So usually that about now, when she gets her first biological solar panels and is able to focus on vegetative growth rather than building a healthy root system. Thtas why its always good to feed your soil, Not your plants.
So in summary i feel that now is the time when she is focusing on VEGETATIVE GROWTH for the first time in her life, kinda. What i mean by kinda is she is always focusing on both, its the only way to survive. This is the first time that she can actually be balanced and have a healthy and secure way (i.e. happy healthy roots) to do the vegetative thing at its full potential . So this is why i feel now would be the time. Just my thoughts.
Happy farmin;)
BTW welcome to the farm my friend.