well she looks about 2 or 3 weeks into flower so i say anytime
i usually do half strength every other watering for a couple of weeks then go full strength every other till flush
i guess it depends on what you are using
Truthfully it doesn't really matter. I've run entire grows on flower nutes with no deficiencies. Current grow I decided to use veg nutrients to see how it does and started flower nutes upon switching to 12/12.