Louth county council came back with a valid additional information request for our application, the time taken from putting it in to receiving an answer was a finite time as we expected it to be and as defined on their web site i.e. 12 weeks for a decision by which time they can request additional information. There was no guessing at how long it would take except if it had happened earlier. I would highly recommend meeting with the planning officer before you put in your application, this way the likelihood of any additional information requests is reduced.