I guess my working theory is that they've already maximized the CM's attendance to the nth degree so adding or subtracting hours (or half hours) is a pretty direct, measurable cost. Everybody's got something to do once they clock in until they clock out, and that that 'something' is relatively important.
It may be a reasonable hunch, that there's a 1/2 hour of 'pad' in the midday somewhere that is acceptable and a one hour pad isn't, to allow for thinning or tapering.
Perhaps spreading the 'early' crowd over four parks rather than one they can somehow make the CM staffing needs much much less? Doesn't seem like it, until they are also cutting back on which areas/attractions are open early.
Even if the expenses break even (rather than double), I think I would still prefer the hour in one park over 1/2 hour in my choice of parks.