A powerful demon from another dimension could be the antagonist. This demon, drawn to the energy of the Hyperbolic Time Chamber, tries to take it over. It has the ability to create illusions inside the chamber, making Goku's training even more difficult and dangerous.
One idea could be Goku discovers a new power within the Hyperbolic Time Chamber. For example, he might accidentally tap into a form of energy that allows him to manipulate time outside the chamber in a very limited way. This new power could be a key to defeating an upcoming, extremely powerful enemy.
The 'locked in time story' could potentially be about a person or a place that seems to be stuck in a particular era. For example, a small town that has preserved its old - fashioned ways and seems as if time has stopped there. It could also be about a character in a story who is trapped in a specific moment, perhaps due to a magical spell or some psychological trauma that keeps them reliving the same time over and over again.
Since I don't know the exact 'locked in time story', it's hard to say. But it could be a young adventurer and an old wise man who holds the key to unlocking the time - locked situation.
A 'locked in time novel' might refer to a story where the characters or the setting is somehow frozen or trapped in a particular moment in time. It could be a time loop situation, where events keep repeating without progression in the overall time line. For example, in some science - fiction novels, a character might be stuck in a day that keeps repeating, like in the movie 'Groundhog Day' which has a similar concept translated into a novel - like narrative.
Goku might run into past versions of his friends. He could see a younger Krillin or Bulma and have some really interesting interactions. He could also meet past versions of his enemies and try to change their fates. For instance, he could meet a young Vegeta and try to steer him away from the path of evil. This would be a huge change in the Saiyan's story.
One possible scenario in this fanfiction could be that Android 18 and Goku are forced to time travel due to a new threat that endangers the entire universe. They might travel to a time when the Saiyans first arrived on Earth. Goku, with his knowledge of the future, could try to change some events to prevent future disasters. Android 18, with her strength and unique abilities, would be a great ally in this adventure. They might face challenges like dealing with the primitive technology of that time and also having to hide their true identities to avoid disrupting the timeline too much.
One example could be 'The Time Traveler's Wife' by Audrey Niffenegger. The story has elements where the characters are sort of 'locked' in different times due to the time - traveling nature of the protagonist. Another is 'Outlander' by Diana Gabaldon, which takes the main character back in time to a very specific historical period where she gets stuck in a way.
Goku's godlike power might make his time travel more precise. Normal time travel in the Dragon Ball universe can be a bit haphazard, but with his godly energy, he could target specific moments more accurately. For instance, he could arrive at the exact second he wants to in the past or future.
If Goku travels back in time, his relationship with Bulma could be very different. In the past, she was more of a guide to him. But if he goes back with his current knowledge and power, he could become more of a protector for her. He might also be able to prevent some of the dangerous situations she got into in the original story.