Across
1 To pass the time (= ELAPSE), electronic engineers start (i.e. first letters of ‘electronic engineers’ = EE) with circuits (= LAPS) inside.
4 Uses up what is 14 across (‘mass-produced’) maybe (= CONSUMER), like fire (= CONSUMER).
9 Seen quite clearly at the Capitol (= CUPOLA), at least fifty (= L) were involved in (indicates anagram) a coup (= A COUP).
10 What one might call 18 across (‘period pieces’) in Atlanta, perhaps (= GEORGIAN)?
12 A cleaner (= SOAP) - Martha, Norma or Lulu, perhaps (= OPERA) - will look at it in the middle of the day (= SOAP OPERA).
13 Use for hose (= NYLON), only in the North (anagram, ONLY and N).
14 What father (ref. priest) brought out during ceremony (i.e. ‘produced’ during ‘mass’) was hardly unique (= MASS-PRODUCED).
18 Stop-starts (i.e. begins with ‘PERIOD’) and in bits at the end (i.e. ends with ‘PIECES’) - very old-fashioned altogether (= PERIOD PIECES).
21 Complex actuarially, giving (indicates hidden word, i.e. ‘complEX ACTuarially) accurate result (= EXACT).
22 Might worried (indicates anagram), religious sister (= NUN) lament (= LAMENT) the break-up (= ANNULMENT)?
24 I hear some are salty (sounds like ‘somersaulty’ i.e. somersault), like this maybe (= BACKFLIP)?
25 Has the most expensive eggs in Russia, perhaps (= BELUGA, ref. ‘Beluga caviar’)
26 Lives here (= DWELLING) in wild glen (anagram of WILD GLEN).
27 Leading carol singers (= C S) around (indicates anagram) here (= HERE) get three (ref. ‘three cheers’) with applause (= CHEERS).
Down
1 It would seem cue (= SEEM CUE) given around ten (= X) was incorrect (indicates anagram) - apologies (= EXCUSE ME)!
2 To evaluate (= APPRAISE) a paper is tricky (indicates anagram of ‘A PAPER IS’).
3 Sudden outburst (= SALVO) from colossal volcano (i.e. ‘colosSAL VOlcano’).
5 Excessive (= OVERBAUNDANT) and odd-looking (indicates anagram) tub on veranda (TUB ON VERANDA).
6 Vast wildlife reserve (= SERENGETI) might be the greenest (= GREENEST) one (= I) around (indicates anagram).
7 That one (= I), on the outside (indicates outer letters), looks quite masculine (= MANLY), by and large (= MAINLY).
8 Confrontations (= RUN-INS) like these make running captains lose heart (i.e. remove central letters from ‘running captains’ = RUNning captaINS).
11 Villification (= DEMONISATION) of Tom in Indonesia (anagram, TOM INDONESIA).
15 What’s 14 across (‘mass=produced’) is this and might give fluent lip (anagram of FLUENT LIP).
16 Various (indicates anagram) clues he’d (= CLUES HED) lined up (= SCHEDULE).
17 Are these ill-made (indicates anagram) trash, say (= TRASH SAY), or are they now regarded as 18 across (= ASH TRAYS, ref. reminiscent of a former time)?
19 Intricately (ref. webbed) connected (= WEBBED) online perhaps (ref. ‘Web’ i.e. internet)?
20 Lacking polish (= GAUCHE), hag (HAG) takes cue (CUE) erroneously (indicates anagram).
23 Adorable echidna might host (indicates hidden word, i.e. adorabLE ECHidna) parasite (= LEECH).