Solution to 1D has been deliberately left unsolved and is to be answered by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
9 Give explanation that is about having luck mostly at a particular time (9) ELUCIDATE {IE<=} over {LUCk} at {DATE}
10 Please point out stupid mistake (5) LAPSE PLEASe*
11 Paying guest has managed to cause extensive damage (5) PRANG {P{RAN}G}
12 Tack of wind instrument section of orchestra/band (9) WOODSCREW {WOODS}{CREW}
13 Cases about volunteers (7) COFFERS {C}{OFFERS}
15 Spooner's listing disease for medicinal case (7) PILLBOX (~bill pox to pillbox)
17 Officials, not rude masters (5,8) CIVIL SERVANTS {CIVIL}{SERVANTS}
21 Carmaker seen regularly at Shell Centre for a petroleum product (7) BENZENE {BENZ}{{sEeN}{shEll}
22 Love to write diary regularly when school is accessible for all (4,3) OPEN DAY {O}{PEN}{DiArY}
23 It prevents one from being caught with pants down (9) SUSPENDER [CD]
25 Past unfolds before the end of title sequence (5) SPATE {PAST}*{t..lE}
27 A goodbye essentially is about love (5) ADIOS {A}{gooDbye}{I{O}S}
28 Girl without a teetotaller attitude or dullness (9) LASSITUDE {LASS}{attITUDE}
DOWN
1 Starting to value! Could be top-secret! (7) ?E?P?C? (Addendum - RESPECT {RESPECT+TO)*=TOP SECRET [CA] Semi&lit - See comments)
2 American soil over Russian body (4) DUMA {A}{MUD}<=
3 Bachelor life scribbled in one line (6,4) SINGLE FILE {SINGLE}{LIFE*}
4 Clergy orders lucrative wars right away (6) FATWAS {FAT}{WArS}
5 Spooner's cushion piece is substandard (5,3) BELOW PAR (~pillow bar to below par)
6 Rich mostly have advantage (4) PLUS PLUSh
7 Sanctioned a very quiet con at Enforcement Directorate (10) APPROBATED {A}{PP}{ROB}{AT}{ED}
8 In the middle of wager, with one to ten thousand at opening (7) BETWIXT {BET}{W}{1}{X}{Th...d}
14 Run into monsters in alliance (10) FRIENDSHIP {F{R}IENDS}{HIP}
18 Harry eats idly little by little (8) STEADILY*
19 Awful bit, baby's malnourished (7) ABYSMAL [T]
20 Small and petty English cunningly prepared content for printing (7) TYPESET {S+PETTY+E}*
22 Surge at happy hours, around mid-morning! (6) ONRUSH {O{morNing}RUSH*}
24 Quarter of naked monsters (4) EAST bEASTs
26 Gang dudes occasionally give chills and fever (4) AGUE {gAnG+dUdEs}
Reference List
Point = E, About = C, Teetotaller = TT, American = A, Right = R, Very quiet = PP, With = W, Run = R, In = HIP, Name = N, Second = S, Small = S, English =E
