Taharos, Chapter 9, Mishnah 4. This chapter walks us through the stages of olive production, from the moment the olives are picked until the oil is pressed, and asks at each stage whether the olives have already become susceptible to tumah. Our mishnah turns to a very practical problem: an am ha'aretz who wants the terumah he separates to reach the kohen in a state of taharah.
"Hagomer es zeisav veshiyer kupah achas." A man has finished bringing in his olive harvest, and one container remains. This last box is not left over by accident: he set it aside deliberately, because that is the box from which terumah is going to come. He is an am ha'aretz, and he knows himself well enough to know that whatever passes through his hands is liable to be handled improperly. So he keeps that box apart from the rest, and the mishnah asks what he should do with it.
It is worth noting where we stand in the process. At this point the olives have not yet become susceptible to tumah, which is precisely why they are still fit to serve as terumah. The completion of the work is marked by his placing them into the container; until that moment, everything we have been discussing about hechsher has not yet taken effect.
"Yitnenah lekohen, divrei Rabbi Meir." Rabbi Meir's answer is the most direct one: hand the box over to a kohen. Let the olives leave the possession of the am ha'aretz entirely and sit under the care of someone who can be relied upon to guard them.
"Rabbi Yehudah omer, yolich es hamafte'ach miyad." In Rabbi Yehudah's view, there is no need for the container itself to leave the owner's hands. It is sufficient that he go without delay and bring to the kohen whatever opens the room in which those olives are stored. What safeguards them is who holds access to them, not who physically owns or carries them.
"Rabbi Shimon omer, me'es le'es." Rabbi Shimon holds that there is no need to act on the spot. He is given a full twenty four hour period in which to see to it, and the olives are not compromised in the meantime.
Three views, then, on the same question: does an am ha'aretz protect the terumah portion by surrendering the olives, by surrendering the key at once, or by attending to the matter within a day?