Using BC's statistics--and I don't dispute those--JonBenet died 1 to 3 hours after she ate the pineapple. There is no firm evidence that she ate the pineapple at the Whites' or in the car on the way home, or at any of the stops along the way, that I'm aware of. Maybe they kept pineapple in the glove compartment--just kidding.
So, she apparently ate it after she got home. If she ate it immediately upon arrival, her parents lied, 'cause they said she was asleep when they carried her from the car up to her room, and didn't awaken when they dressed her for bed. Interestingly, in DOI, John doesn't say when they got home, though he says they left the Whites' at approximately 8:30 PM. But, he does say they put JB in bed first, then he put Burke to bed at around 9:30 PM; so, I don't suppose JB was up eating pineapple from the bowl under discussion at that time.
John says that after putting Burke to bed, he went upstairs, got ready for bed, took a melatonin, set the alarm for 5:30 AM, got in bed, read a while, then fell asleep. How much time was consumed in all those activities? Here, again, we're forced to estimate (that is if we don't refer to the interview transcripts or police reports, etc.).
Let's say John was fast asleep by 10:00 PM. Patsy was already in bed , John said. Let's assume that she, also, was asleep by that time. Now we have two soundly sleeping parents, well out of earshot of any post tuck-in snacking going on in the kitchen.
Let's assume that the kids hopped out of bed shortly after John zonked out at 10:00 PM, raced to the kitchen, and began gorging themselves on pineapple and tea.
Since it takes a while for food to get from bowl to mouth to stomach, and there was more than 1 microgram of food consumed, let's estimate that the all the food consumed had entered JB's stomach by 10:15 PM.
One hour later or 3 hours later, depending on which figure you choose, JonBenet is dead. So, she is dead at 11:15 PM or 1:15 PM, your choice.
The unsub has plenty of time--from 1 hour to 3 hours, to arrive on the scene, nab JB, and kill her. How her body got down to the basement is anybody's guess.
Just my opinion....