Exode 2:23

And it was after many of those days that the king of Mizraim was struck (with disease), and he commanded to kill the firstborn of the sons of Israel, that he might bathe himself in their blood. And the sons of Israel groaned with the labour that was hard upon them; and they cried, and their cry ascended to the high heavens of the Lord. And He spake in His Word to deliver them from the travail.

AND IT CAME TO PASS IN THE COURSE OF THOSE MANY DAYS. Scripture uses the expression “in those days” or “on that day” only when alluding to a brief current event, but of a past event it says, and it came to pass afterward. In that case then, it should have said here, “and it came to pass afterward that the king of Egypt died.” It is for this reason that our Rabbis have said that because they were days of suffering [for Israel], Scripture calls them “many” although alluding to a brief current event. — instead of saying “in those days.” To a suffering people — as Israel was at that time — even a brief period appeared as a long one. So also have the Rabbis said in connection with the above-mentioned verse, And it came to pass in those days when Moses was grown up, that his growth was unnatural, meaning, sudden and fast. alludes to a brief current event. Hence when it says in the case of Moses’ growth, and it was in those days and Moses was grown up, the Rabbis interpreted it to mean that his growth was brief and sudden. Under all circumstances, the period [covered in the verses], and the king of Egypt died, and the children of Israel cried out and their cry came up unto G-d, was [altogether] a brief period of time.
However, we might also explain that in the course of those many days refers to the days of suffering and hard labor which were exceedingly many, as the exile became very prolonged. It was this [long period of suffering and hard labor] which caused them to cry out, and their cry came up unto G-d. Similarly, the verse, And it came to pass after many days, the word of the Eternal came to Elijah, in the third year, means that there were many days [of famine] and afterwards this event, [related there in the Book of Kings], occurred.
In my opinion, the purport of this verse, [And it came to pass in the course of those many days], is to allude to those days when Moses was a fugitive from Pharaoh. Indeed he was but a youth when he fled, as the verse said, And when Moses was grown up he went out unto his brethren, suggesting that immediately when he grew up and became self-conscious and they told him that he was a Jew, he longed to see the burdens, toils and oppressions of his brethren. On that [first] day on which he went out, he smote the Egyptian, and on the second day, they denounced him [to the authorities] and he fled. He was thus at that time approximately twelve …

ויהי בימים הרבים ההם, after Moses had slain the Egyptian and Pharaoh had tried to execute him for murder, and Moses had fled from his presence and remained in hiding until he was 80 years of age when G’d decided to speak with him, the King of Egypt who had tried to kill him died (only now). The Children of Israel had merely groaned under his persecution all this time. G’d now saw their suffering, while Moses during all that time had been a shepherd of his father-in-law’s flocks. At that time G’d appeared to Moses and commanded him to return to Egypt (3,1). Moses was unwilling to return to Egypt as he was still afraid of criminal proceedings against him, until G’d told him (4,19) that there was no cause for this, as all the people who wanted him dead had already died themselves. This is why the Torah reports here וימת מלך מצרים, so that we would understand what 4,19 is all about. The entire literary construction is similar to Genesis 9,18 וחם הוא אבי כנען. [verses 19-21 after that are in parenthesis before the Torah continues about Cham. Ed]

בימים הרבים ההם, from the day Moses had fled from Egypt in his youth until Gershom had been born when he was close to 80 years of age. We are assuming that Eliezer was not much younger, and we know that he was only born when Moses was already on his way back to Egypt. We know that that Moses was 80 years of age t that time.

וימת מלך מצרים, the same Pharaoh who had been pursuing Moses wanting to execute him. This is why he called his second son Eliezer, as then he realised that he had finally been saved by G’d from the sword of Pharaoh.

ויזעקו, they cried out of frustration about their miserable fate and their enslavement. A similar expression for venting such feelings of frustration occurs in Isaiah 14,31הלילי שער זעקי העיר, “Howl, o gate! Cry out, o city!”

ותעל שועתם אל האלוקים מן העובדה. G’d’s response was not due to their repenting and praying, but He simply was angry over the excessive cruelty with which the Egyptians treated the Jewish people This is why He added (when He spoke to Moses in 3,9) וגם ראיתי את הלחץ אשר מצרים לוחצים אותם, “and I have also seen the pressure that the Egyptians keep imposing on them. [perhaps the reason why our author does not consider the Jews’ repentance and prayer being a factor is the fact that the attribute with which G’d responded was still the attribute of Justice, אלוקים and not the attribute Hashem as he explained to Moses in 3,9 Ed.]

וימת מלך מצרים, the King of Egypt died;” as long as that king had been alive, the Hebrews had been hoping and praying all the time that he would die soon. They hoped against hope that his anti-Hebrew decrees would die with him. When none of his decrees was annulled even after his death, they sighed; they realised that there was no relief in sight and for the first time in 86 years they turned to their G–d in prayer. An alternate interpretation: they felt that their potential leader Moses would now be able to return to Egypt without having to fear an indictment. G–d also used this opportunity of their prayer to reveal Himself to Moses at the bottom of Mount Sinai, at the burning bush, setting in motion the process of their redemption.