If all goes well and the parts come off easy to get to the wheel bearing especially a front wheel drive car then it could take a couple hours to disassemble the car down to the parts needed to remove the wheel bearing.
If it's stubborn like I've had a few of them do then it can take 5 hours or more to get the wheel bearing off.
It depends on the car and how tight things are on the car. Some parts come off easy and others are a pain to get apart.
The wheel bearing replacement is not the hardest part to replace but it's the getting the rest of the parts out of the way disassembled that causes the most trouble.