7  One convict returned for celebration (4)

 8  Recalibrate fine hearth temperature measurement scale (10)

 9  Study, when retired, about a king without clothes (5)

12 Impressionism in the absence of noir components may lead to despair  (9)

15 Donkey follows mischievous child with energy resulting in deadlock (7)

16 Preserve, including part of rib and spine (7)

20 Right after the beginning of the second/third day of the week, in short? Correct! (4)

21 Long, no? Coming after 12 months (5)

23 Immediately after this, knight, remove covers from texts (4)

24 Container to hold donations of minced lambs and animal (4,3)

27 Prolong porridge time (7)

29 Remember, to some extent, last name of West German chancellor and painter (9)

32 Old word processor (sometimes on laptop?) mistyped notes (5)

35 Snap John's enthusiasm at first and come apart (5,5)

36 He's into South Dakota's garden construction (4)

 2  <=> Interchange File Format in short (3)

 3  ((Fourth of 16 + fourth of 8 + fourth of four + sixth of 12) by fifth of 15) or 60% of ... (5)

 4  Come on, it's just a trailer (6)

 5  Electronic radio operator's ICAO code for Schipol Airport (1,1,1,1)

 6  Poses displaying oomph on board (4)

10 Drake, perhaps, mixed a dram with milk endlessly (7)

11 Time to have endless intercourse, using initially red scented rubbers (7)

13 Annoy Inland Revenue clerk at last (3)

14 See English mole (4)

17 Agreement despatched by jailbird (7)

18 Roman law symbol book useful to puzzle solvers (7)

19 CIA's confused about this group briefly I hear (1,1,1)

22 American Bill's remark: A bit of money for a bit of music (4)

25 Silent female ancestor (3)

26 Prophetic deity's Spanish exclamation about reversing vehicle (6)

28 Nowadays, head office primarily communicates for this in Latin (2,3)

30 Setter's in before Erin (4)

31 God! Gangster's chasing graduate! (4)

33 Resounding event - it can be heard just before Foxtrot (4)

34 Brief reference to part of Mysore forest (3)