balance charging 20s 12p battery????????

Does anyone know roughly how long it should take to balance charge a 20S 12P battery pack after the charger light turns green? Batteries are Sanyo 18650GA, charger is Luna 72 volt 150amp and the BMS is SuPower Battery (batterysupports.com) 20S 150amp.
I just replaced the first cell group and after installation it is out by approximately 0.2 volts. My pack charges to 80.4 volts, the charger light goes green and the charger stops. Last time, after charger light turned green, I left it on 3-4 hours and the voltage of my battery stayed the same. I'm thinking more time to balance but I have no idea.

that is a huge imbalance can take days and in the meantime you are slowly killing your cells.
manually discharge the cells that are too high.

I start with a balance batery before installation of the BMS the BMS is to keep a balanced pack in balance. Pull down the highest cells with a lightbulb try to get it in order it's just a little itty bitty BMS it just looks big and powerful.

you can discharge them by hooking up a car headlight bulb for example or charge them manually with a dedicated charger.
or you can crack a powerbank and hook the leads up on that and charge each group that way.

Thanks for the input. I'm discharging the high cells now.
Hopefully now my BMS will work properly and keep it balanced now that the cells are closer.

If the charger never turns itself back on during the balancing process, the time it will take is eternity.

If it won't restart on its own, what you have to do is let the bms work, discharging high cells for about 30 min after the charger goes green. Then unplug and replug to make the charger start back up. if it won't start, ride around the block, and then recharge.

It could take many many many repeats of this cycle, depending on how out of balance it is.

Once balanced, it should stay reasonably balanced, just by charging once, and letting the bms drain any high cells. Do the forcing it to balance more only when you have been hammering the pack, like discharging till it is 100% empty.

Thanks all. I drained my high cells and my charge is now up to 83.1 volts. The first four cells are now just 0.02 volts high. After I drained the high cells they were all the same which means the cells that were high went high again. When my charger is fully charged and green it will not turn back on for the balance step of the process. So, I'll try manually unplugging after 30 mins. and then plug back in to see if I can get this fine balance process going.