Time taken to solve: Off the scale but not as bad as for last Sunday's puzzle (my worst ever at 2 hours). I knew I was in for trouble when I noticed the grid had long answers at the perimeter and nothing with fewer than 5 letters. LH  went in reasonably easily (about 20 minutes) but I struggled every inch of the way RH. There were some easy answers on that side, particularly in the SE but my brain had seized up by then. I didn't know the cube or the cow or the sprite or the cloth definition at 19ac. Here we go:

Across
1	SPIT-AND-SAWDUST - Anagram of PINT SAID then SAW (spotted) DUST (evidence of poor cleaning). This is a simple old-fashioned type of pub with sawdust on the floor.
9	SABREWING - SING (tweet) swallows A BREW (a drink). It's an American hummingbird apparently.
10	NIXIE - More Americana here with NIX (nothing) then Irritate Except. It's a water sprite that has managed to elude me until today.
11	ADULT - A DULl T
12	TESSERACT - TEST (exam) contains CARES (worries) reversed. It's defined by Chambers as a cube within a cube. COED and Collins have never heard of it so I had difficulty verifying my answer once I had worked it out from wordplay.
13	NED KELLY - Anagram of LookeD KEENLY. The Australian outlaw.
15	MISTED - To ted is to spread out grass for drying so MIS-TED is to do it wrongly.
17	BOVVER - puB,OV(V)ER. This is a corruption of the word 'bother' - to make trouble - which in the 60s gave us  'bovver boys' and then 'bovver boots'.
19	PRUNELLA - PRUNE (cut),L,L,A. I knew this as a plant but not as a fabric until this morning.
22	LIBERTINE - Anagram of REBEL IN IT.
23	SNAIL - kisS,NAIL
24	TWANG - GNAT (one biting) reversed encloses Western. It's a nasal way of speaking in certain accents and dialects.
25	FLOOR SHOW - FLOORS (confounds), H (husband), OW (it's painful).
26	BOSTON TEA PARTY - Cryptic definition that took me for ever to see.
Down
1	SUSTAINABILITY - Anagram of IS SUITABLY ANTI
2	Better leave one out…
3	…and another to make up for nothing in the Acrosses.
4	DAINTILY - DAILY (paper) encloses I, New Testament (set of books).
5	ARGOSY - A, ROSY encloses Grand. It's a merchant ship or a fleet thereof.
6	DANDELION - DAN (Judo expert), OILED (drunk) reversed, New. Not the kind of wine that I would like to drink, thank you very much. It has reminded me of Reggie Perrin's son-in-law although he was capable of producing even worse concoctions.
7	SEXTANT - Sailor, EXTANT
8	BELTED GALLOWAY - Anagram of GOT LABELLED then WAY. I wasted forever on this clue trying to include COW in the anagrist to make a journey.
14	EYEBRIGHT - It's a plant used to treat certain eye conditions. The reference in the clue is to the saying 'Bright-eyed and bushy-tailed' meaning alert and sprightly. According to Brewer's this dates from the 1940s as a stereotypical image of a squirrel and was popularised in a song of the same name from 1953 by Bob Merrill. I've  never heard of it or him despite my interest in that sort of thing.
16	GRUESOME - Sounds like 'grew some'.
18	VIBRATO - VIOlin (instrument in half) encloses BRAT (badly-behaved child).
20	LEATHER - Large, ETHER (number) encloses A (article).
21	TIFFIN - TIFF (row), IN (among). A light lunch from the days of the Raj to remind me again of the Noel Coward song referred to yesterday.
23	STRIP - ST (saint, so 'holy'), Rest In Peace.