your plants are fine,some plants tend to change colour quicker than others, for instance orange bud and blue widow can look ready to harvest at 5 or 6 weeks, others will retain white hairs for much longer, trichomes are a certain way of checking although many experienced growers dont bother checking them, its all down to experience we just chop when we feel like it. thc will be on your plants after about 4 weeks and u can chop and smoke them but they'll be weaker and wont have produced there full potential yeild . for an indica 8 weeks is always a good yardstick to have a look and see. you may decide to give them a week more. your choice.