Fast charging is just an alternate way of delivering power through standard 5V USB lines.

Regular USB lines are rated at 5V. To allow transmitting higher power without ramping up the amperage, you add voltage instead.

This creates a problem that the same connector now comes in higher voltages, which older device may not be able to withstand and will just fry if clueless users plug them into the new charger.

So There is a series of protocols to authenticate between the charger and the receiving device before it switches to fast charging, without authentication, the charger only outputs at 5V.

For charging time, OP did not provide enough information, like the model of the phone, charging from what percentage to what percentage and the temperatures. Charging will become slower above 80 and even below 80 if the temperature is out of the safe range.