Prospect of official document — and time to fill it (5)
I believe the answer is:
vista
'prospect' is the definition.
(synonyms)
'official document and time to fill it' is the wordplay.
'official document' becomes 'vi' (I can't explain this - if you can you should believe this answer much more).
'and' means one lot of letters go next to another.
'time' becomes 't' (abbreviation).
'to fill' means one lot of letters goes inside another.
'it' becomes 'sa' (old-fashioned abbreviation for sex appeal).
't' placed inside 'sa' is 'sta'.
'vi'+'sta'='VISTA'
'of' is the link.
(Other definitions for vista that I've seen before include "A view as seen through a long narrow opening" , "Perspective" , "Panoramic view" , "View (with avenue)" , "Broad prospect" .)