
Any one has any idea how much time it takes to get promoted from C3B to C4 ? And what's the criteria for it ?

It may take something between 3 years to forever. Some people are C3B even at 25 YOE.
In good old days, it used to take around 2 or 3 As and a good working relationship. Now it may take minimum 3-4 As (sometimes B in between) and lot of other factors like contributions to account or horizontal, leading key programs, customer facing and internal leadership position, very niche technology skill expertise.

Criteria is how much value do you create and how is that being advertised and how account DP and CP perceive your value. More perceived value and more rigorous follow ups, sooner you will get it.

It is not an easy promotion.
Service Delivery managers who manage 100+ people are in C4.
Maybe if you show potential that you can do that job and if your manager gets promoted leaving that position vacant, it might happen.
I remember reading it in promotion policy document that c4 needs some geography level approval.

Just checked the policy document.
C4 (and equivalent) and above grades will need additional review

better to look outside