She literally can't wait to start her journey today. She's been bouncing around in her room all night, though she has had to keep it quiet. If her dad knew that she was going to go get her very own pokémon and start her journey, he'd probably have a heart attack and lock them both up in the basement. He really doesn't want her to go.
But Juliet knows that this is important. She's been waiting for this moment her whole life! Ever since she saw her uncles battle each other when she was really little, she has known that that is what she wants to do. She literally can't wait for it. So... she sneaks out of her house - it's super easy, even with her dad's Braviary, Palamon, keeping watch, and super-spies all the way to town and the professor's lab. The fact that it's nearly one o'clock in the morning doesn't matter.
Juliet thinks for a moment about waking Hartley up and bringing him with her but dismisses it because she knows he'll be grumpy about it. Plus he doesn't even care about pokémon anyway and this way she'll get ahead in their game.
She knocks of the Professor's door and then keeps on knocking when no one answers. She can do this all night.