During the battle of Aizen VS Shunsui, Soi-fon and Toshiro, at the end when Toshiro impales Aizen on his sword the barrier that was protecting Izuru and the injured Soul Reapers came down and Momo started to walk off in like a trance.
at that time Ichigo yells out what everyone was doing revealing that the entire time Aizen had activated Kyoka Suigetsu and Toshiro had just impaled Momo while the Momo that was with Izuru was in fact Aizen.
But when did Aizen switch with Momo? because
- the answer to This question says that Kyoka Suigetsu was activated from the start
- Ichigo wasn't under the hypnosis of Kyoka Suigetsu which is why he could see that they had just stabbed Momo
- Momo had been in the barrier getting treated by Izuru
- There didn't seem to be any signs that Aizen had broke though the barrier to switch places with her
- When the Garganta opened and Ichigo returned he didn't hesitate to attack Aizen (though he did hesitate to use his Hollowfication but that was a different matter)
So do we know or can work out when Aizen switched with Momo to escape being stabbed by Toshiro?