So lithium ion batteries are charged in two stages.
Stage 1 is constant current, usually between 0.5 and 1 amps.
Stage 2 is constant voltage, held at the cells fully charged voltage, typically 4.2V. This stage lasts until the current into the battery is about 10% of the stage 1 current.
It doesn't make a huge difference in total charge time what current is used in stage 1...higher current makes stage 1 shorter but stage 2 longer.
The better charger ICs on the market disconnect from the battery at the end of stage 2, but do provide a maintenance charge when the cell voltage drops below about 4 volts. This is not harmful to the battery.
The nitecore is a good charger, you can leave your battery on there as long as you want, it won't hurt anything.