Last night the same fares that have been available for the last fair while were still in the system. As of today, it appears that basically all but some very expensive fares have moved to a model that allows flying on any day but only in certain times of the day, notably 7am-noon on the return SFO-BOS segment.

All flights I've tried to price out regardless of date flying back on say, the redeye, have shot up to $931 or so.

Any idea what the problem is?