If an airline has a choice of delaying one flight by 8 hours or two flights by 4 hours each, they’ll take the former every time. There are three reasons for this, and you can prioritize them in whichever order you wish: (a) it impacts fewer passengers; (b) in most cases, the marginal impact of a passenger being delayed 4 hours vs 8 hours is less than the marginal impact of being on-time vs delayed 4 hours; and (c) the most common on-time statistic is presented as a percentage, not an average arrival time relative to par.

But WineCountryUA makes a good point; the fact that UA has an input into the matter does not mean that they have control over it.