I know this is not popular here but even 9 o'clock would be stretching normal digestion. For nothing to reach the duodenum it is odd after one hour. If the girls ate by 6:30 or even 7 some chyme should have been there by nine.
That's the whole point. It IS unusual for a meal started at 6.30pm to still be entirely within the stomach at 9pm, but it's unusual-to-the-point-of-impossibility for this to be the case at 10pm or beyond.
In fact, statistics suggest that for otherwise healthy adults, a meal still sitting entirely within the stomach some 2.5 hours after the start of ingestion occurs in around 2-5%* of the population. Unusual, yes, but nowhere near impossible.
And it just so happens that Kercher must have fallen into this category, since we know she cannot have died before 9pm, and since we know with pretty good confidence that she must have started her pizza & apple crumble meal by around 6.30pm. As a reminder, we know for certain that the food matter found within her stomach must have been the entirety of that last meal, since no other food matter was found anywhere else in the duodenum, jejunum or remainder of the small intestine right up to the very end of the small intestine where a very small amount of food matter was found (which would have been the product of food eaten at least 6-7 hours before death, and which almost certainly was the snack Kercher ate at the cottage before she set out for her friends' house that afternoon).
But - and this is the critical thing - for that 2-5%, if one follows the statistical curve, almost all of this group will have started transit to the duodenum within a further half an hour, and all of the remainder will have started transit to the duodenum within a further half an hour after that.
So, given that we know Kercher
must have been in this 2-5% group at the "far end of the bell curve", we can also say that it's hugely likely that she died before 9.30pm, and a practical certainty that she died before 10pm.
* Different studies suggest slightly differing bell curves, but this is the margin of error, and the shapes of the curves remain constant.