I understand that UA sometimes increases / decreases inventory in various fare classes based on demand (ie. they may shift some availability from higher to lower classes or add more "R" when demand for a particular flight is lower than projected, and vice-versa when demand runs higher).

Is this solely an overnight thing, or does it happen throughout the day? Does anyone know what time a nightly adjustment occurs - assuming there indeed is one? Would be both interesting and helpful to know.