6s is 25.2v, so 40 amp* or 10 amp/per. About 3.5C rate, so 20 minutes is about 1C of charge or a full battery from 20%. He may have meant from storage, so far less amps needed. Chargers are amperage limited on input and output, and wattage limited. PL8 is 1344 watts at >26v input and only 612 W at 12 v. Of course the time will be affected by taper off charge.
4 x 6s (25.2V) x 2.8 ( or your 1C number) is 282W is I calculate correctly. Chargers are not 100% efficient, so allow 300W, but should be easily doable. I can't make sense of your numbers, but check my calculations.
*I don't remember, but don't think that you can hit a full 40 amp with that battery load.