What Jesus was saying is that his disciples must work while it is day because within 40 years the Son of Man would return. In other words, the disciples could never rest on their laurels, slap themselves on the back and retire. But when the Son of Man came, the harvest would come and their work would be complete. In the meantime they were to be servants whose master is expected back at any moment, so they stay busy:
[Luk 12:36-37 KJV] 36 And ye yourselves like unto men that wait for their lord, when he will return from the wedding; that when he cometh and knocketh, they may open unto him immediately. 37 Blessed [are] those servants, whom the lord when he cometh shall find watching: verily I say unto you, that he shall gird himself, and make them to sit down to meat, and will come forth and serve them.
For more information I recommend this gentleman's videos (with thanks to Gina for recommending them to me).
The old covenant was destroyed in 70ad in the war with Rome and Jerusalem, the temple and 1/3 (Zechariah says 2/3) of the Jews were destroyed in terrible judgment:
Joel 2:1-17 [KJV]
1 Blow ye the trumpet in Zion, and sound an alarm in my holy mountain: let all the inhabitants of the land tremble: for the day of the LORD cometh, for [it is] nigh at hand; 2 A day of darkness and of gloominess, a day of clouds and of thick darkness, as the morning spread upon the mountains: a great people and a strong; there hath not been ever the like, neither shall be any more after it, [even] to the years of many generations [IE: Rome!].
3 A fire devoureth before them; and behind them a flame burneth: the land [is] as the garden of Eden before them, and behind them a desolate wilderness; yea, and nothing shall escape them. 4 The appearance of them [is] as the appearance of horses; and as horsemen, so shall they run. 5 Like the noise of chariots on the tops of mountains shall they leap, like the noise of a flame of fire that devoureth the stubble, as a strong people set in battle array.
6 Before their face the people shall be much pained: all faces shall gather blackness. 7 They shall run like mighty men; they shall climb the wall like men of war; and they shall march every one on his ways, and they shall not break their ranks: 8 Neither shall one thrust another; they shall walk every one in his path: and [when] they fall upon the sword, they shall not be wounded. 9 They shall run to and fro in the city; they shall run upon the wall, they shall climb up upon the houses; they shall enter in at the windows like a thief.
10 The earth [IE: the land of Israel] shall quake before them; the heavens shall tremble: the sun and the moon shall be dark, and the stars shall withdraw their shining: 11 And the LORD shall utter his voice before his army: for his camp [is] very great: for [he is] strong that executeth his word: for **the day of the LORD [is] great and very terrible; and who can abide it? **
12 Therefore also now, saith the LORD, turn ye [even] to me with all your heart, and with fasting, and with weeping, and with mourning: 13 And rend your heart, and not your garments, and turn unto the LORD your God: for he [is] gracious and merciful, slow to anger, and of great kindness, and repenteth him of the evil. 14 Who knoweth [if] he will return and repent, and leave a blessing behind him; [even] a meat offering and a drink offering unto the LORD your God?
15 Blow the trumpet in Zion, sanctify a fast, call a solemn assembly: 16 Gather the people, sanctify the congregation, assemble the elders, gather the children, and those that suck the breasts: let the bridegroom go forth of his chamber, and the bride out of her closet. 17 Let the priests, the ministers of the LORD, weep between the porch and the altar, and let them say, Spare thy people, O LORD, and give not thine heritage to reproach, that the heathen should rule over them: wherefore should they say among the people, Where [is] their God?
Please see this also which may or may not support my post. Feedback welcome:
b. with ἄν and the aorist subjunctive (equivalent to the Latin future perfect), where it is left doubtful when that will take place till which it is said a thing will continue (cf. Winer's Grammar, § 42, 5): ἴσθι ἐκεῖ, ἕως ἄν εἴπω σοι, Matthew 2:13; add, Matthew 5:18; 10:11; 22:44; Mark 6:10; Mark 12:36; Luke 17:8; Luke 20:43; Acts 2:55; Hebrews 1:13; after a negative sentence: Matthew 5:18, 26; Matthew 10:23 (T WH omit ἄν); Matthew 12:20; 16:28; 23:39; 24:34; Mark 9:1; Luke 9:27; Luke 21:32; 1 Corinthians 4:5; with the aorist subjunctive without the addition of ἄν: Mark 6:45 R G; Mark 14:32 (here Tr marginal reading future); Luke 15:4; (Luke 12:59 T Tr WH; Luke 22:34 L T Tr WH); 2 Thessalonians 2:7; Hebrews 10:13; Revelation 6:11 (Rec. ἕως οὗ); οὐκ ἀνἔζησαν ἕως τελεσθῇ τά χίλια ἔτη, did not live again till the thousand years had been finished (elapsi fuerint), Revelation 20:5 Rec. Cf. Winers Grammar, § 41 b. 3.
Bottom line: Yes there are differences in the punishment of different people based on differences in the dispensation, the crime, the victim, etc.