Hi - sadly, there is no "average" or rule of thumb for completing a S106 - the negotiations and timescales will depend on the number and complexity of issues involved.
A few points though. First, although we don't know the full details, you will probably find that legally, you don't have a planning permission yet - you probably only have the Council's "resolution" to grant planning permission at this stage. The actual grant of planning permission will not occur until after the S106 has been agreed and signed. Second, this is important because if the planning circumstances have changed since April 2016 (eg land supply position or policy changes) then the Council will be within its rights (possibly legally obliged) to look at their decision all over again. Third, you should make sure you keep your option to appeal open in case you can't reach agreement on the S106.
Have you agreed to pay the Council's legal fees for their input and/or have there been any surprises in negotiations compared to what was identified before you submitted the application (assuming you discussed S106 matters before submission)?
Good luck pushing this forward.
Andy
