The charge times can vary depending on how low the battery charge is when you begin recharging.
If the battery has quite a bit of charge already, the lights will turn green more quickly (indicating the cell is fully charged) than if the charge has been depleted. In this case it may take up to 4 hours - or even over night - to fully charge, depending on how low the charge was to begin with.
CAUTION: The battery should always be allowed to come to room-temperature before charging. Charging the battery in extreme heat or cold might delay charging or damage the battery/charger. For best results, try to charge the battery at temperatures between 50º and 80ºF (10º-30ºC).
NOTE: When you first plug the battery into the charger the lights will initially turn red. Even if the battery is only slightly used. Once the cell is fully charged, the light for that cell will turn green.
Once all three lights turn green, that indicates the battery is fully charged.