ok i placed fishing net over water dug out another 3+ blocks under the net and placed a small crate over the net. Am i doing something wrong here?

The fishing net needs to be placed over water with a storage container somewhere around it, like stated in the book.
Then you need to wait, it takes a long time to catch a fish.

Please explain further if you think there is a bug occuring here, otherwise close this issue.

estimate how many minecraft days does it take to have one catch?

so far we have weighted 3 minecraft days for the net to catch a fish.

At least 15000 ticks, so about one Minecraft day.

-k- one sec

I can't reproduce this.
Post a screenshot of your setup.

under the net is over 3+ blocks of water. Directly above the net is the crate.

it just caught a fish.... after posting this.