How did Hermione go to classes with the Time-Turner if she couldn’t be seen?

Question

If no one is supposed to see you when you use the Time-Turner, how did Hermione go to classes then? She obviously didn’t hide anywhere because Ron asked other students if she was in all classes, and she was.

Answer 1

They couldn’t be seen because they were breaking the law.

Dumbledore warned Hermione not to be seen for two reasons: she was only permitted by the Ministry to use the Time-Turner for her classes, and she certainly wasn’t supposed to use it for freeing fugitives.

“Now, pay attention,’ said Dumbledore, speaking very low, and very clearly. ‘Sirius is locked in Professor Flitwick’s office on the seventh floor. Thirteenth window from the right of the West Tower. If all goes well, you will be able to save more than one innocent life tonight. But remember this, both of you. You must not be seen. Miss Granger, you know the law – you know what is at stake … you – must – not – be – seen.”
_{^{- Harry Potter and the Prisoner of Azkaban, Chapter 21 (Hermione’s Secret)}}

It was also a wizarding law that wizards shouldn’t try to change time.

“No!’ said Hermione in a terrified whisper. ‘Don’t you understand? We’re breaking one of the most important wizarding laws! Nobody’s supposed to change time, nobody! You heard Dumbledore, if we’re seen –’
_{^{- Harry Potter and the Prisoner of Azkaban, Chapter 21 (Hermione’s Secret)}}

She was allowed to use it for her classes by the Ministry, which also meant the Ministry knew she had one.

“I’ve been using it all year to get to all my lessons. Professor McGonagall made me swear I wouldn’t tell anyone. She had to write all sorts of letters to the Ministry of Magic so I could have one. She had to tell them that I was a model student, and that I’d never, ever use it for anything except my studies … I’ve been turning it back so I could do hours over again, that’s how I’ve been doing several lessons at once, see?”
_{^{- Harry Potter and the Prisoner of Azkaban, Chapter 21 (Hermione’s Secret)}}

So, she couldn’t risk being seen and then known to have changed time, as well as being connected with the freeing of Sirius and Buckbeak by the Ministry.

In general, lawful use, you’re only not supposed to see yourself.

The only restriction on her Ministry-sanctioned use of the Time-Turner would probably be that she couldn’t see herself.

‘We’d only be seen by ourselves and Hagrid!’

‘Harry, what do you think you’d do if you saw yourself bursting into Hagrid’s house?’ said Hermione.’

‘I’d – I’d think I’d gone mad,’ said Harry, ‘or I’d think there was some Dark Magic going on –’

‘Exactly! You wouldn’t understand, you might even attack yourself! Don’t you see? Professor McGonagall told me what awful things have happened when wizards have meddled with time … loads of them ended up killing their past or future selves by mistake!”
_{^{- Harry Potter and the Prisoner of Azkaban, Chapter 21 (Hermione’s Secret)}}

However, it is possible that since she’d know she had a Time-Turner before she started using it, she’d be able to get around this because she’d never see herself before she’d be aware of having one, and therefore not surprised by seeing herself.