It is easier to work with an earlier flight but I've never had any problem with going standby on a later one. Contrary to some assertions, your ticket does not disappear after your first flight leaves the gate. Just in case you run into a nasty agent, I would suggest a call to NWA asking them to to note on your record that you plan on taking a later flight in accordance with their same day standby policy. Shouldn't really be a problem after this.....