I personaly use Maxibloom thru entire grow.If you need to feed the 12/12 stretch for large plants then check Gh's website for schedule.
I think the previous poster is right about 50/50 Maxi grow/bloom for 12/12 transition.
I use 5 grams (3/4 tsp) per gal for under 400 watts,and it is recommended 7 grams (1tsp) pg for higher watt hids.
p.s. by the 2nd-3rd or more (strain dependent) week Nitrogen is less needed when stretch stops.