The shutdown would take effect tomorrow if it happens. Congress will stay in session (but their staffers may have to go home, and I am not sure who will feed them in the cafeteria...). The post office has their own separate revenue stream, they will stay open. Your local schools do not get any money from the federal government, so they should stay open. Last time it happened was in 1995 (impact I noticed at the time was a snafu in a merger/acquisition project I was working on, as the Dept of Justice couldn't move forward on approval for the business deal-- the delay cost us a bunch of money).