It has to be after Toun arrived - Edit 1
Before modification by Rurouni_Kenshin at 12/10/2009 06:50:08 AM
She's near the city, but she hasn't reached it yet. Moreover, it would still be only 40 days after Semirhage told Suroth about the assassination, Ebou Dar might not have heard yet, or only just received the information.
At the day of the arrival of the new Empress, may she live forever, to Ebou Dar it was common knowledge in the city - reread KoD Epilogue. And one could think that such news would spread rather quickly. As for just received them, I agree, but that rules out 'three days after'.
Otherwise Surouth and Galgan would be discussing the attack on Tylee's army. Galgan mentions that he just promoted her but says nothing of her being attacked. Tylee in her POV mentions just being raised to the Low Blood. So it must be after Toun's return.