I might even allow a bit more time. We recently had bookings of YVR-LAX on UA and LAX-PTY-UIO on CM and it took a substantial amount of time. I also believe it's even harder when both bookings are on United, but I haven't done that (yet). The key there is to find an agent who knows how to use SHARES, because that's apparently the only way to do it. Our agent had to be walked through it by a more senior agent.