On average a person needs at least 7 hours of sleep to function in the day and have good health.
Some people may need 8 to 10 hours of sleep to be healthy and be alert and able to function the next day.
It is possible to sleep too much and too much sleep can actually sometimes be worse than too little sleep.
Too long to sleep would be around 14 hours or more unless you're really tired.
If you find yourself sleeping more during the day then you might have a health condition that causes it.
So if you're sleeping too much through the day or sleeping too much at night then let a doctor know about it because there are some health conditions that cause that.
But as long as you're not sleeping more than 12 to 13 hours per night then you're usually not sleeping too much.