8 weeks into flower - do brown pistils mean it’s almost ready

It won’t open up like a regular flower, it will just add size and density as it grows. How long has it been in flower, and also just judging the pistils isn’t the best way to see if they’re ready for harvest. Buy a jewelers loupe or some sort of magnifying glass so you can look at the trichomes, that’s the only for sure way to see if she’s ready or not.

 

Looks like u still got a few weeks atleast

 

You need to look at the over all picture. If the plants still pushing out white pistils it's still growing and maturing. Once that has slowed down it's time to check the trics for the final say on harvest time.

 

Your plants show signs of nitrogen toxicity. Back off the nitrogen or you will affect the yield even more.

 

Look a bit heat stressed

 

Native Jamaican see should be sativa, but I doubt there is any pure anything outside of the jungle anymore. That being said, you would be looking at more of 10 to 11 weeks, depending on the indica percentage.
As mentioned above, watch the trichs... For an "up" product, a bit less than 50% amber, for couchlock, 80% amber. It's not rocket science... Best guess is usually fine.

Now, for next time...
With the space you have, your yield should be several times more than you have there.
I see some of the normal degradation a flowering plant will encounter, but there is more.
I see a heat/humidity issue, a light issue, insufficient root space, insufficient veg time.
The feedings appear to be good, but a bit strong. I would suggest reducing the concentration 20%. In almost all cases with cannabis, less is more. They will produce on a surprisingly small quantity of nutrients. Maximizing yield and plant health takes time, experience and experimentation/failure.
I can't really see the medium you are growing in, but it appears to be soil. If so, those pots are half the size they need to be. Remember, that pot is the only environment where the plant can access minerals and water. If the space cannot hold enough for a full cycle, the plant will suffer. My 4 plants, when in full flower use 5 gallons in about 4 days. (full hydro so water usage monitoring is easy.)

The internode spacing on those plants looks quite excessive to me. This is due to insufficient light, especially during the stretch. This is important because it is at the node and only at the node that a bud will develop.
With LED lights, you have a very limited (compared to HID) canopy penetration of the light. This means that the effective light sufficient for good plant growth only extends for a short distance from the lights. I haven't fully tested this, but it seems that 14 to 18 inches is about all you can expect from LED's, realistically.
This requires one to alter the growth of the plant or adjust their methods to compensate. With LED's, a very compact plant is most suited. Cannabis is difficult to keep compact. SOG techniques would work well here. Veg for 3 weeks and ensure ALL the branches are under the screen before flowering. You should be able to fully fill your space with buds in the 8 to 10 inch range. A system like this would let thoseLED's really shine.
Keep the lamps as close as possible... Light falls off at the square of the distance. If you have a light of a given strength at the bulb, it will be pretty much the same for a foot away, at two feet, it is one quarter of its strength.... at three feet it is one ninth... and so on...

The heat/humidy issue will need more discussion to work out a decent solution.

Here is a picture of my latest grow at day 19 of flower. Three different strains. White Widow (in the back right), Purple Kush (front left) and an unknown bagseed, probably an AK or similar...
I know there are some issues with the grow... Was balancing nutrient requirements of three very different strains while dealing with hardware failure.
Even if you really screw up, you can have a decent harvest.