It's unlikely that a baby will self-wean at 6 months, so I wouldn't worry about that. As long as you keep giving milk first before solids, she shouldn't fill up too much on them and not get enough milk (unless you're really giving big portions - for the first year, solids are more for practice than for real eating...). During the day, she is likely just more distractible, so eats less - 5-15 min sounds fine though. With respect to the 6 oz, babies eat about the same amount of breastmilk at every feed at 6 months as they do at 1 month (different from formula!) - so even if she's eating less per feed during the day, she's likely getting enough.