Seconds Out by Nibor

Taking a hint from the title, the second letters of the extra words in clues spell out START CENTRE TOP GO DIAGONALLY FORMING A CLOCK. Accordingly, the words SPACE ODYSSEY can be found in the grid, with the 12 letters in the approximate positions of the numbers on a clockface. The title is a reference to the book and film 2001: A Space Odyssey, although Gregson, for one, was concerned by the existence of the other sequel odysseys in 2010, 2061 and 3001.

To finish the puzzle, solvers had to draw two lines on the grid. Gregson took the title as a further hint that these should be the hour and minute hand on the clock, with the second hand omitted. There then followed hours of agonising over just how accurate these needed to be. What worried Gregson as much as anything was the fact that the letters are not strictly in the right place, since they do not mark 30° equiangular sectors. An unnecessary worry, since the solution indicates that anything with the minute hand longer than the hour and the hour pointing roughly at the 8 o'clock S and the minute hand just right of vertical at the 12 o'clock S was acceptable. Given how precise and accurate solvers are normally expected to be in the Listener, this final ambiguity seems to let down what is otherwise a fine puzzle. However, it appears that the puzzle was amended by the editors late on and did not appear as Nibor intended it.

In the following explanations the extra words in clues are shown in [square brackets].

ACROSS
1 Sailor's [useless] barley sounds difficult to take in (8)
ABSTRUSE (ABS (sailor's) + homophone for TRUCE (barley))
6 Proof of divinity lessons with [strict] priest coming first (5)
REPRO (RE (divinity lessons) + PR priest) + O (of))
10 Hair [partly] twisted back in a flap causes problem with vision (7)
LEUCOMA (LOMA (flap) round CUE (hair twisted) rev)
11 Brahma's [breathless] counterpart on earth's heard by some to go on and on loudly (6)
YAMMER (homophone for YAMA)
12 [Stop] reckless pop, flying after tenor, say, landing on tummy (13)
BELLY-FLOPPING (BELL (tenor) + anag of POP FLYING)
13 Sceptically - [scarcely] like a philosopher (6)
ASKANT (AS (like) + KANT (philosopher))
16 Works for two [feet], expected to tickle ivories to start with (6)
DUETTI (DUE (expected) + TTI (first letters of to tickle ivories))
18 Second mowing makes [Indian] grass change sides (4)
RAWN (LAWN (grass) with L (left) replaced by R (right))
20 [Stendhal] lovers are rather dry indeed (8)
AMORETTI (A (are) + MORE (rather) + TT (dry) + I (indeed))
21 Companies stay involved, falling [crazily] into group with common warning colours (13)
SYNAPOSEMATIC (anag of COMPANIES STAY)
22 Brighter, extremely cute rector secures [second] prize (8)
CLEVERER (CE (first and last letters of cute) + R (rector) round LEVER (prize))
26 Being inferior, [stupidly] loses both hands (4)
ESSE (LESSER (inferior) minus L (left) and R (right))
28 Reform the duplex structure of a [wounded] fish, so it's said (6)
ANNEAL (homophone for AN EEL (a fish))
30 [Specialist] umpire tucks into a cooked meal - not kosher (6)
TEREFA (TEA (cooked meal) round REF (umpire))
32 Variegated, [ugly] - mucks up your old carpet (13)
PARTY-COLOURED (anag of YOUR OLD CARPET)
33 Sign of error in City - leaders of every party traumatised bar [none] (6)
EXCEPT (EC (City) round X (sign of error) + EPT (first letters of every party traumatised))
34 I [admit] a sabre can be deployed to make someone Semitic (7)
ARABISE (anag of I A SABRE)
35 Where Ed might have written [final] part of Shephearde's Serenade? (5)
DESSE (hidden)
36 [Japanese] mountain boy has endless sacrificial feast (8, two words)
ID AL-ADHA (IDA (mountain) + LAD (boy) + HAS minus last letter)

DOWN
1 French town's heartless excuse for [ignorant] failure (4)
ALBI (ALIBI (excuse for failure) minus middle letter)
2 Give more power to retainer, say, in [your] local rising (6, two words)
BEEF UP (PUB (local) round FEE (retainer) all rev)
3 State of gloomy anger unless [incorrect] lens is changed (10)
SULLENNESS (anag of UNLESS LENS)
4 Revels before second [gay] Tory's out (6)
ROYSTS (anag of TORYS + S (second))
5 Its berries are edible - part of crust's nearly all [pleasant] (5)
SALAL (SAL (part of crust) + ALL minus last letter)
6 Fierce dinosaur caught in trap [alleges] torture (6)
RAPTOR (hidden)
7 Unfurnished [byre] - timeless, truly heavenly (8)
EMPYREAL (EMPTY (unfurnished) minus T (ie timeless) + REAL (truly))
8 [After] split take cottage room in Scotland (4)
REND (R (take) + END (cottage room))
9 Old mechanical car I [took] along for a spin (9)
ORGANICAL (anag of CAR I ALONG)
14 Short aperitif with a distinctive character sounds [brilliant] - cheers! (6)
KIA-ORA (KIR (aperitif) minus last letter + A + homophone for AURA (distinctive character))
15 Limousine can pass this [omnibus], but not if lacking energy! (10, two words)
CATTLE GRID (cryptic def - a limousine can pass but a limousin can't)
16 DDR disintegrated with pieces [rightly] separated (9)
DISCERPED (anag of DDR PIECES)
17 Destiny - more than one important date in a short time? [Unlikely] ecstasy! (6)
MOERAE (MO (short time) + E (ecstasy) round ERA (important date))
19 French shuttles distributed at [Egyptian] events (8)
NAVETTES (anag of AT EVENTS)
23 City [ladykiller] to symbolise reproduction (6)
ECTYPE (EC (City) + TYPE (symbolise))
24 Expecting brief intelligence on a [scruffy] lecturer (6, two words)
IN FOAL (INFO (brief intelligence) + A + L (lecturer))
25 Ruler of kings [plugs] interminable joke - a cheer goes round (6)
RAJESH (RAH (cheer) round JEST (joke) minus last letter)
27 Upset father - examination has learner failing in Highway [Code] (5)
A-ROAD (DA (father) + ORAL (examination) minus L (learner) all rev)
29 Light blue chopper [scares] enemy at first (4)
SAXE (SAX (chopper) + E (first letter of enemy))
31 Exclamation of dismay on losing ends in [skittle] halls (4)
ODEA (OH DEAR (exclamation of dismay) minus last letters)