10 minutes before so that you have enough time to put the stuff from your desk in a box before you walk out the door. :) All joking aside it depends on what pr

10 minutes before so that you have enough time to put the stuff from your desk in a box before you walk out the door. :) All joking aside it depends on what projects you are working on and how friendly your superiors are. If you are leading projects that cannot be easily picked up, and your superiors are friendly, you might want to give them a month notice so that your last month can be spent passing on crucial knowledge and shifting you out of projects that depend on you. Generally giving 2 weeks notice is all you need as that is required to get vacation and stuff paid out. ( in the USA at any rate )