6th week :
The plants are 35-40 cm high, have 6 layers of leaves and look very healthy.
I think, i can go ahead and make autumn to them by changing the light cycle to 12/12.
Surely they'll grow at least twice as much, so it should be fine.
7th week :
The plants have rapidly accelerated their growth - they grow 2-3 cm every day.
@DrJones,
I have a thermo-hygrostat (the one for a power socket). If the humidity is above 55%, then it turns on the heater and fans at higher speeds. This allows me to maintain the right humidity (between 45-55%).