grower error wise (just possibilities) the only things i can think that would do that are maybe the rockwool was too moist for the strain, or more likely in this case was too much light too early on, burning leaves or again more likely roots... idk... you may be right on with bad seeds.
as for maturity, 5-8 is generally there but if the strain likes long seasons outdoors, 10-14 weeks is not unheard of. its pretty rare though.
It should mature faster from seed if you follow my kind of schedule as flowering is caused by the buildup of the plants hormones that are produced at night. notice how its normally 5-12 days before it starts flowering when switched from 18/6 to 12/12. the more mature the quicker the switch also points toward this.
i start seeds under a t5 in perlited soil.
i use the following light cycles to speed up maturation, slightly increase stretch if i want to mainline or have a set height im aiming for ie scrog screen, and to save power.
seeds start on 15/9. i used 5 oz cups this run that i cut to increase air pruning. you use your methods but use just the t5's till day 14 then switch to just the mh for 2 weeks, then combine spectrum on day 28-35.
day 14 i switch to 14/10 to increase chances of female
https://cannabisgrowing.wordpress.com/2012/09/06/top-7-tips-to-grow-more-female-plants-from-standard-cannabis-seeds/. by now all seedlings have left 5-10 oz cup for ~3.75 quarts of soil. in your case, this is now mh only time.
day 28 if im rushing the plants, i switch to 12/12, if im vegging for a monster, i switch to 15/9 or 16/8. now is okay to add all the lights, esp in dwc.
day 35 if vegging add another 1-2 hours. keep light cycle on 16-18 hours and should show maturity 1-2 weeks sooner during veg. if flowering, preflowers should be showing soon if not already.
