If you bought a new one it should be charged, used one I usually left on over night the check with meter.
Yes, an overnight charge would be well over 6-1/2 hours.
Still, lead acid batteries can show full voltage after charging for two or three hours. However, that's not enough to provide the full rated current output over the full rated period. For example, it might provide a full amp, but for only two or three hours instead of the rated five. Granted, most feeders only pull a few milliamperes at most, meaning a 5 amp hour battery can easily last several weeks. Much of the power that is lost is used to turn the motor.