My cell phone says it will regain 100% charge after 8 hours. Is this normal (first charge) for a cell phone fast charge? And what to do in the opposite case?
thanks in advance

If using the original charger and usb cable, you should charge your device in approximately 2.5 - 3 hours depending on the use of the device while charging it.
The estimated time that you read on your graph is, as its name says, an estimate. Don't take it's number as 100% real.
Charge your phone and you will see the correct time