Have you even read the instructions?

A 1C charge is where the charging amperage matches that of the battery. ie, a 4000mah battery = 4 amps therefore theoretically it should take one hour to charge. However the charger is programed to start reducing the current once the battery voltage reaches 4.2v/cell. That is typical of a constant current constant voltage charger.

Usually once the 4.2 volt threshold is detected the battery is 90% charged. The last 10% could take as long as the first as the charger balances each cell if you are balance charging.

Now add to that the fact that you will not be discharging a lipo below 3.0 volts/cell means that the battery has charge left in it so in your example it could hace 1 to 1.5 amps left so you are only putting in less than the total capacity of the pack.

See how easy that is and it;s all in the manual too for your future reference.