Boy am I glad to know that I'm not the only one "foggy" about this. I know that Little's attack took place late in the afternoon (4 or 5?) and that by this time of year the days were getting shorter. My guess is that sunset was maybe around 6:30. That being said, here are my thoughts:
1. Due to the hour, Price may have been unable to get his entire force up and engaged before dark.
2. I don't remember for sure, but had Price's cavalry reported Ord's presence off to the Northwest? If so, he would have likely held back a significant portion of his available force to meet that threat.
3. I think it is pretty well agreed that Price wanted to continue the fight the next morning. If they had the intelligence regarding Ord, it is likely that his subordinates used that in their argument to break off and join forces with Van Dorn.
4. Where did the arms that the Rosecrans claimed to have captured come from? Were they truly Confederate arms that Price brought with him, or were they arms that Price had recently liberated from Grant's stores at Iuka, thereby merely changing hands once again?
I'll have to go back to old sources, and/or try to find some new ones to refresh that foggy memory.