Knives out laundry scene logic

Question

One scene of Knives Out is totally out of otherwise magnificent plot with concise logic. What happened in the laundry at 1209 Columbus Rd before 10AM?

As the movie says after using a huge overdose of morphine you have about 10 minutes before you die. That is absolute key premise for the whole plot. How could Ransom possibly inject morphine to Fran within 10 minutes before 10 am or any close to it? As he was with Marta discussing the report etc. including car chase, to finally be captured by the police. Or how could Fran in the laundry possibly be still alive when found at that time by Marta, long long time after huge overdose of morphine?

My take: The only way I see it is fatal error in the plot. Marta had to find Fran alive to make the final scene more dramatic, and to bluff Ransom to make him confess. So 10 minutes limit simply went out of the window, or should I say main premise of the plot went out of the window.

Answer 1

At 8am or so, Ransom meets Fran in the laundry (as per her original blackmail note). He doses her with morphine, ties her up, stages the scene, and leaves to meet Marta. Marta gets there around 10am.

What's been established in the movie previously is that injecting someone with the amount of morphine that Marta thought she'd injected Harlem with is fatal in 10 minutes. Ransom may simply injected Fran with less morphine or in a different body part. He's not a medical professional.

From harmreduction.org, about opioid overdoses:

Opioids fit into specific receptors that also affect the drive to breathe. If someone can not breathe or is not breathing enough, the oxygen levels in the blood decrease and the lips and fingers turn blue- this is called cyanosis. This oxygen starvation eventually stops other vital organs like the heart, then the brain. This leads to unconsciousness, coma, and then death. Within 3-5 minutes without oxygen, brain damage starts to occur, soon followed by death. With opioid overdoses, surviving or dying wholly depends on breathing and oxygen. Fortunately, this process is rarely instantaneous; people slowly stop breathing which usually happens minutes to hours after the drug was used. While people have been “found dead with a needle in their arm,” more often there is time to intervene between when an overdose starts and before a victim dies.

Answer 2

I have discussed this with multiple people, including nurse, and came to this conclusion:

First there is huge difference between intravenous and intramuscular injection - Marta to Harlan intravenous vs Ransom to Fran intramuscular injection. With intramuscular it usually takes way way longer for substance to get into blood system.

Second as mentioned in answer I accepted, Ransom uses way lower dose - looking closely at scenes - 3 ml syringe vs 10 ml syringe Marta uses with Harlan. So in micrograms calculation based on Marta's "100 overdose vs 3 intended" this would convert into approximately to 30 micrograms with Ransom using full 3 ml syringe. Which is still 10 x more than "standard" dose.

Combined effect of these could possibly prolong Fran's life enough to be found by Marta alive at around 10 am, about 2 hours after Ransom did the injection.