I don't want to discourage you, so don't take this the wrong way, but that's a pretty large amount of time for a beginner to practice all at once. That kind of endurance takes a good while to build up in most players.
When you play, you are not supposed to bite the mouthpiece to make a sound, but use your facial muscles to make a seal around the mouthpiece instead. As players become more tired, the tendency is to start biting.
Especially as a beginner, be aware of this as you practice for extended periods of time, as it will become habit if left unchecked. Being careful to avoid bad habits early on will go a long way.