In brief we have a few basic rules:
Create 3+ videos per month
Tag them properly
Comply with AUP (no illegal, sexist, racist, uneconomic content)
Then you join the pending queue, we are manually checking accounts on a daily basis.
For this we must go through every profile individually and look at your account, channels, content stream and check if your tags are fitting to what is being played in your stream/video.
This process takes depending on the accounts more or less time. If there are some issues it is slowing the accreditation down and we must go through those accounts multiple time.