It requires a substantial amount of resources to be successful.
Therefore, places that can alter the flow of time are quite rare.
Although Heavenly Immortals also comprehend the Time Law, they can only momentarily change the flow of time.
To change it for a long duration is basically impossible.
Because the immortal power within a Heavenly Immortal can't withstand prolonged consumption, nor can it handle excessive pressure.
"That's right, indeed the Time Book House exists."
"Our human cultivators use the power of the Time Book House to learn a vast amount of knowledge."
"After all, truly learning these things would take at least hundreds of years, even several centuries."
"But staying in the Time Book House, only a few hundred days are needed."
"This can't even begin to quantify how much time it saves us in learning."
"Saving time on learning is equivalent to extending our lifespan."
