slow flowering

hey i have my 3 unknown strain bagseed from some decent bud, its like 4 weeks into flowering and i got like nickel and dime size nuggs formed randomly around the plants but nothing more.. their under 2x400w HPS lamps, and i was looking aorund at other pictures 4 - 5 wks into flowering and mine looks kinda .. retarted? as far as the rate.. im using miracle grow flowering ferts as well... does the flowering rate kick in at a higher rate the last 1/2 of its flowering period or are these going to take 3 months to flower enough for my efforts? lol