Ok, here's my operational theory: main points are
-the flights have to depart and arrive into a local hub;
-an airline wants its aircraft on the ground as short as possible, for sure the ground time abroad should be minimized;
So, here are my 2 scenario's:
1-If the extra ORD flight were to be operated by AA, the operational sequence would start in ORD, where AA has 2 main international hubs, namely around 4.30-5pm and around 8.15-8.45pm.
Given the departure time of the SR flight at 4.15pm, the second flight would have to start at the later hub, and arrive in ZRH somewhere around 11.30am the next day, right in front of the 12 o'clock SR European hub, which would make sense. (Btw the AA operated ORD-BRU flight has the same structure).
Minimizing the ground time in ZRH to about 2 hours, the flight could leave again around 1.30pm, and given SR has a Japan/China hub around 2pm, the flight would most likely leave at that time, as around 1.15pm an inbound European bank of flights, providing ample feeder service is available.
The flight would then arrive around 5.15pm in ORD, in the middle of AA's second internartional arrival wave, with a connecting hub about 90 minutes later.
2-If the would would be SR operated, the airline would like to leave as late as possible, but still in time to catch the last main hub at ORD, giving pax the opportunity to reach any destination in the US the same day.
They would leave also late for their own operational purposes, creating more flexibilty to perform a/c changes and so on.
The flight would then depart probably in SR's late afternoon US hub, where there's also the SFO, EWR and 2nd BOS flight, as well as the JED flight, and for which feeder service is available at the 3 o'clock inbound european hub.
The flight would then arrive in ORD around 7 pm, still in time to catch the last main AA hub, and leave again for ZRH around 9-10 pm, just after an inbound domestic AA hub, arriving in ZRH around 12.30pm or so, together with the late JFK arrival, in time to catch the 2pm european hub.
You think this makes sense?