FCOD is not usually linked to standby. Standby, for passengers, is very restricted, it does happen, but usually there is an irrop or airline failure of some sort. Most standby passengers are crew / company staff on staff travel. Unlike in the USA. FCOD therefore either gives you a confirmed seat or not. However there could easily be a lot of changes between midnight and departure, not least those on FCOD on early flights wanting to go later. So never say never, but FCOD -> Standby is not an advertised option or something that happens in normal circumstances.