Hey there, the first sign of white hairs after the switch to 12/12 is the day you are supposed to start counting flowers, after the plant reaches its 10-12 hours of darkness it starts to prepare for the hormonal changes, it normally takes roughly 4-7 days after the switch before you start to see white hairs. Most energy for the next 2 weeks will be spent on getting as much of the plant into "PRIME" conditions for flower, flowering requires more reds and stronger light for bountiful blooms so the plant will "stretch" to get as many stems into that hot zone, by week 5-6 all vertical growth will grind to a halt.
If you are new to growing, stick to what's working in terms of feeding, and flowering the plant can get sensitive, nitrogen is the most delicate of the nutrients when it comes to toxicity make sure 0 nitrogen is fed after week 4 ish.
Looks good, doing great, keep up the good work.