18650 pack with many series BMS for faster charging?
0.5c is relative to the entire pack, assuming the individual cells capacity is well matched, so for your 14s4p battery, your pack capacity would be 4 times that of your average cell capacity, e.g. 3000mAh cells would be a pack capacity of 12000mAh, this is what the 0.5c is based on, Having batteries in series only increases the voltage you have to charge with,

If you put 2 cells in series, the voltage has increased, but has the same capacity, so if you feed in 0.5c amps, both charge at the same time, 

If you put 2 cells in parallel, the voltage is the same, but the capacity has increased, so 0.5c is now twice as much, so you feed in double the current, and both charge at ~0.5c 

So it will be roughly 2 hours to charge at 0.5c, however if there are cells with large differences in capacity making up the pack, the balancing while charging will increase this time,