Ready by when?

Answer 3 is a great deal less clear or natural than any of the other versions.

Things are completed 'in' (such and such a) time in English; or, for greater emphasis on the speed and deadline, we can also say 'within'.

Answer 3 is the standard, familiar version.
Answer 1 would suggest you then cease observing, at the very moment you move into potential danger; hardly very sensible! Likewise, Answer 2 suggests stopping at some point during your crossing, which is surely even more dangerous; checking afterwards (Answer 4) is all very well, yet surely somewhat pointless?

Answer 2 does the best job of linking the two ideas in the time-perspective that the speaker fairly clearly means; 'when ... ' (Answer 1) does not make this so clear or ironic, Answer 3 is a good try but not grammatical, and 'during ...' (Answer 4) can only come in front of a noun or noun-group, but not a clause with a verb in it. ('During the performance', but 'while she was performing'.)

Plenty of good time-link words on offer here, but only Answer 3 matches perfectly in both blanks.

If it still wasn't over by 6 o'clock, and did not finish beyond that either, we can have no idea quite how long it did continue. At least with the other Answers we know that they were still playing at 6 o'clock, but there is the implicit assumption that they finished the match sometime after that.

Answer 3 is different, because it suggests that once the man retires, he WILL be able to pay back the money (perhaps out of a 'lump sum' when he begins to draw his pension); the others each imply that he will have to continue paying, even once his pension becomes his only income (rather than out of earnings).

Actions last FOR a length of time and DURING a wider timespan. All the 'wrong' first-blank Answers would probably be understood, but none of them is good accurate English; we can say 'at' or 'over' the weekend (or even, in American English, 'on the weekend'), but we would only usually do this with the very next weekend coming up. One that were further into the future, and dated as such, would more likely be introduced by 'during'.

Answer 4 is 'neither quite one thing, nor the other'!

All the '1st-blank' answers are good except at No.4; 'but' (Answer 3) is a good clear conjunction with much the same force, here, as 'until'; but only Answer 2 is acceptable for the 3rd blank ~ and indeed, all through.
'The Noughties' is a fairly commonly accepted nickname for the first decade of the 21st (or indeed any) century: you will probably be used to such usages as 'the fifties' (ie the 1950s) and 'eighties hairstyles' (eg of HRH Princess Diana during the 1980s). There was then, though, a bit of a gap in English: what should we call the decade whose last-but-one number was a zero? (ie, 2000-2009.) The word 'noughties' suggested itself, possibly by transference from the 'naughty nineties' (originally, the 1890s ~ believe that or not!), and with the inbuilt pun on 'nought' ( = '0') and 'naughty' (ie characterised by bad or risky behaviour).
Meanwhile, Oxford University numbers the weeks of its working terms from First Week to Eighth Week, but the preparatory week when the students arrive and get themselves organised is known administratively as Noughth Week.