Charging a dead phone usually takes around 2 hours.
If your phone is only half dead and you have around 30 percent to 50 percent charge in the phones battery it may only take around 1 hour to charge.
You can also leave the phone plugged in all night or when you're at home and not using it to keep it charged.
When I'm at home I always keep my phone plugged into the charger to keep it fully charged at all times.
Never had any issues with leaving the phone on charge all day or all night.
This ensures that I never worry about my phones battery being too low as it will always have a full charge.
Your phone is equipped to turn off the charging to the phone's battery when it's fully charged so the phone will not overcharge if left plugged in and charging all the time.
It's best to keep your phones battery at least half charged instead of being completely dead too.