from the time you submitt your planning application to a notification of a decision to grant or refuse is usually 8 weeks. if you receive planning permission after the 8 weeks, then you must wait another month to get the final grant, after which you can leagally begin on site (having put in all relevant commencement notices, etc.). of course, on the day before the 8 weeks is up, they may come nack and ask you for additional information, once this is submitted to then, a decision is made 4 weeks later. unless they ask for clarification of the additional information! so, to summarise: the shortest lenght of time for planning is 8 weeks + 4 weeks for final grant + 2 weeks for commencement notice.