2 Samuel 24:10 David was conscience-stricken after he had counted the fighting men, and he said to the Lord, “I have sinned greatly in what I have done. Now, Lord, I beg you, take away the guilt of your servant. I have done a very foolish thing.”

11 Before David got up the next morning, the word of the Lord had come to Gad the prophet, David’s seer: 12 “Go and tell David, ‘This is what the Lord says: I am giving you three options. Choose one of them for me to carry out against you.’”

13 So Gad went to David and said to him, “Shall there come on you three(b) years of famine in your land? Or three months of fleeing from your enemies while they pursue you? Or three days of plague in your land? Now then, think it over and decide how I should answer the one who sent me.”

14 David said to Gad, “I am in deep distress. Let us fall into the hands of the Lord, for his mercy is great; but do not let me fall into human hands.”

15 So the Lord sent a plague on Israel from that morning until the end of the time designated, and seventy thousand of the people from Dan to Beersheba died. 16 When the angel stretched out his hand to destroy Jerusalem, the Lord relented concerning the disaster and said to the angel who was afflicting the people, “Enough! Withdraw your hand.” The angel of the Lord was then at the threshing floor of Araunah the Jebusite.

17 When David saw the angel who was striking down the people, he said to the Lord, “I have sinned; I, the shepherd,[c] have done wrong. These are but sheep. What have they done? Let your hand fall on me and my family.”

b. 2 Samuel 24:13 Septuagint (see also 1 Chron. 21:12); Hebrew seven
c. 2 Samuel 24:17 Dead Sea Scrolls and Septuagint; Masoretic Text does not have the shepherd

Now it's easy for me to get confused. The "options" as I read them are three years famine, three months running, or three days of plague. Then I read in verse 15 that it says "until the end of the time designated". When I first read this this morning.... I read "until the end of time designated".... see I left out the "the" and got all messed up.... so don't do that please.... The end of the time and the end of time are two different animals.

This is from enduringword.com.

Please let me fall into the hand of the LORD: This meant that David chose the three days of plague. In the other two options the king and his family could be insulated against the danger, but David knew that he had to expose himself to the chastisement of God.

“Had he chosen war, his own personal safety was in no danger, because there was already an ordinance preventing him from going to battle. Had he chosen famine, his own wealth would have secured his and his own family’s support. But he showed the greatness of his mind in choosing the pestilence, to the ravages of which himself and his household were exposed equally with the meanest of his subjects.

Do not let me fall into the hand of man: This meant that David chose the three days of plague. In the other two options, Israel would either be at the mercy of neighbors (as in the famine) or attacked by enemies. David knew that God was far more merciful and gracious than man

Seventy thousand men of the people died: This was a great calamity upon Israel – a devastating plague striking so many in such a short period of time.

Let Your hand, I pray, be against me and against my father’s house: Like a true shepherd, David asked that the punishment be upon him and his own household. Having another purpose to accomplish, God did not accept David’s offer.

This is from bibletrack.org.

Behind door #3...a plague! But it's only for three days though - and it's from God rather than from David's enemies (that was door #2). The pestilence costs David 70,000 men, but falls short of the destruction of Jerusalem. As a matter of fact, the angel in charge of pestilence stops at the threshing floor of Ornan the Jebusite as David pleads for mercy. This threshing floor becomes very important in Jewish history as it becomes the site of the Temple.

So... did the Pestilence end early? Yep.... this is from biblehub.com.

Verse 15. - Even to the time appointed. This rendering, though very uncertain, is retained in the Revised Version. It would mean, of course, the end of the third day, as the pestilence was to last for that time. The objections to it are that there is no article in the Hebrew, so that literally it would be "unto a time appointed." Secondly, the pestilence did not continue unto the time appointed, but was mercifully stayed.

Prayer worked..... That was a horrible pestilence.... killing 70,000 men in less than three days! I googled "what pestilence would kill 70,000 in three days".