High MrCarpy,
You can start feeding them now and feed them everytime when you give water. You start with a low EC 1.0 and you build this up by + EC 0.1 every week till you reached EC 1.8 (do not give more then EC 1.8). Continue giving EC 1.8 till she is ready for flushing before harvest.
When you add products in a later stage then never start with the full amount but do this with steps. Do the same when you want to cut a type of nutritions.
So example you give 2 ml nutritions for grow but you see the first flowering signs so you want to change to flowering nutritions. Then you still give 1.5 ml grow and 0.5 ml flowering nutritions. The next time you give 1 ml grow and 1 ml flowering, then 0.5 ml grow and 1.5 ml flowering and then full amount flowering nutritions. Do this with every type of change and nutritions that you want to use. Plants hate changes so you need to do things step by step!
Happy Growing! 😋