How long should chia seeds soak? I am new to use chia seeds.
   I soaked them in water for about an hour and there was no significant difference in the size.

As per websites it could grow like 12 times the original size.

How much time does it need to be at its maximum size?
I usually let it soak overnight, though it isn't necessary to soak that long. You should soak it till it forms a paste/gel like consistency and it would take at least  2-3 hours, though this website claims under ten minutes (time might vary depending on the batch of the seeds). You could also soak it in any juice or fruit extract as well.

Additionally, you can also use it in its raw form without soaking, the way one would use poppy/sesame seeds.