Your hobby shop was correct, and you are correct in noticing that it's taking longer than they said it should take. At the rate you are charging your 6300mAh battery it should take 6.3 hours to charge.

The maximum charge or discharge rate of a battery is directly proportional to the capacitance of the battery. Lithium Polymer batteries can be safely charged at a rate of "1C", which means "1 times the capacitance". Your battery has a capacitance of 6300mAh or 6.3Ah (Amp * Hours).

An amp*hour means this... The battery will last 1 Hour if discharged at a rate of 1 Amp. Your battery is 6.3 Amp Hours, which means it will last 6.3 Hours if discharged at a rate of 1 Amp. Another way to look at it is: it will last 1 Hour if discharged at a rate of 6.3 Amps.

Here's the bottom line: Your battery's capacitance is 6.3 Amp * Hours. Because it is a Lithium Polymer battery, it can be charged at a maximum rate of 1C. Therefore you can safely charge your battery at a rate of 6.3 Amps. If you charged the battery at 6.3 Amps, then it will take 1 Hour to charge. However, you are currently charging the battery at a rate of 1 Amp, so it will take 6.3 Hours to charge.

Hope that helps.