Originally Posted by
grepdashv
That query wasn't even remotely exotic. It was just a round trip between cities that have relatively limited routes between them. Seems very unlikely that the query would have wandered into infinite space and timed out, especially for only a subset of days within the calendar.
At least in the past (and we're going back quite a few years) I had a similar query and was told that some of the routing codes and extensions codes were applied as a filter after the searching was complete. So although you think you're helping the engine by narrowing the parameters, it is really the number of potential travel days that matters. When you click on a particular day, the engine re-runs the analysis on the single day and has time to find more results.
The problem space really is vast (formally it's not merely N-P hard but computationally undecidable), even for a single city pair on a small number of days. So the engine applies heuristics, that sometimes works against what we as a human know can be done.