I would say between 10-12 years.

However, in the new system implemented this year, "time norms" have been discarded somewhat. Where previously an officer must have served a certain number of years in a grade before he/she becomes eligible to be promoted, it is not the case now. So good officers can progress faster, but average/poorer performing officers may stay at their grades for longer. So it could look like 8-15 years now.