I don't know if there is a "standard" length? I remember reading somewhere not to cut motor wires, to de-solder them because the length was critical.
I spliced the three motor wires on two different ESCs that are in two different planes, the Clouds Fly (similar to the SkyS) and a flying wing. I have not noticed any problem with either spliced ESC and I have more than 50 flights on each machine.
On one splice I simply extended the three ESC wires by soldering on a length of wire to each ESC motor wire, no added connectors in the middle of the wire.
The second ESC (flying wing) I extended the 3 wires by building three wires with connectors on each end (male on one end, female on the other) and using these three wires with connectors to go between the 3 ESC motor wires and the brushless motor wires.
Both methods have worked so far. Hope this helps.