You got the story a little wrong there. Bane won first choice, and choose Tyranny. Myrkul was next and chose the Dead, telling Bane that all things, even gods, will eventually fall under his dominion. Bhaal chose last, picking Death. He claimed he held the upper hand, since he could rob Bane of his subjects by killing them, or deny Myrkul his due by NOT killing anyone.
As for time, I've never run across any mention of the exact time they ascended. Sometime after the fall of Netheril sounds good to me.
As for time, I've never run across any mention of the exact time they ascended. Sometime after the fall of Netheril sounds good to me.