Hardly descriptive of the time a final demand arrives (3-6,3)
I believe the answer is:
red-letter day
'hardly descriptive of' is the definition.
The definition suggests a singular noun which matches the answer.
'time a final demand arrives' is the wordplay.
I cannot quite see how this works, but
'time' could be 'day' (day is a kind of time) and 'day' is located in the answer.
The remaining letters 'redletter' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'the' acts as a link.
Can you help me to learn more?
(Other definitions for red-letter day that I've seen before include "Special occasion in calendar" , "Noteworthy time" , "Momentous date" , "Memorably important occasion" , "Special date in the calendar" .)