How long does it take to charge a LiPo battery?

It depends on the capacity of the battery and the current that the charger delivers to it.

If you have a 1000mAH battery, and the charge current is 1000mA, it’s going to take about an hour to go from 0% charged to 100%.

If the charger supplies twice as much current, it’ll take half as long to charge it, so at 2000mA it’s going to take about 30 minutes.

It’s not as exact as that: a LiPo charger doesn’t supply a fixed current, and charging a battery isn’t 100% efficient, but it should give you a rough idea.