Weariness leads to early night; nobody's up before one (5)
I believe the answer is:
ennui
'weariness' is the definition.
(ennui is weariness or boredom)
'leads to early night nobody's up before one' is the wordplay.
'leads to' suggests taking the first letters.
'before' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
The first letters of 'early night nobodys up' is 'ennu'.
'ennu'+'i'='ENNUI'
(Other definitions for ennui that I've seen before include "Boredom, languor" , "Effect of boredom" , "Feeling when tired of life?" , "Bored listlessness" , "French boredom and lassitude" .)