I imagine it will have an air lock system. You wouldn't pressurize/depressurize the whole track. Just small sections at the beginning and end of the ride. You would board, and then the train pulls forward to a section of track that seals off from both the station and the rest of the track. That section is vacuumed then doors to the vacuum sealed rail open. Train moves out.

Then when nearing the next station the reverse is done. Train pulls into a section that is then sealed and pressurized. Then pulls forward into the station where people get off/board.

Assuming they would vacuum and pressurize the whole rail is silly. That's like if they decided to depressurize the whole space station every time someone had to do a space walk. That's not how that happens. The train would take up most of the space in the air lock section so there wouldn't be nearly as much air to remove. It would probably take less time that you would spend boarding a commercial flight.