The sooner towards the lights coming on, the more the plants can use it. Plants only use carbon and ferts during lighting periods, so putting it in 2 hours before the lights go off is sort of pointless. It's like putting out a 4 course meal at 1am when everyone is just going to bed. It's just going to sit on the table and rot all night.
No i think i said something wrong. I can't put it right before lights on. But i can put it a few hours before, not after the light go out.