High time (4)
'high time' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for noon that I've seen before include "See 8" , "when PM starts" , "Twelve o'clock, midday" , "when only mad dogs go out?" , "A moment of time" .)
(Other definitions for mass that I've seen before include "congregate for > service" , "Ceremony for many" , "Celebration of the Eucharist, especially in the RC Church" , "Accumulation" , "state, in short" .)
'high time' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for boom that I've seen before include "Floating barrier" , "Report" , "Loud noise - business increase" , "Crash" , "time of 22 [PROSPERITY]" .)