Holiday time in lieu is every so often uncertain? No! (7)
I believe the answer is:
leisure
'holiday time in' is the definition.
'leisure' can be an answer for 'holiday' (thesaurus). I am not sure about the 'time in' bit.
'lieu is every so often uncertain? no' is the wordplay.
'every so often' means one should take alternating letters.
'uncertain? no' becomes 'sure' ('sure' is the opposite to 'uncertain').
'lieu'+'is'='lieuis'
The alternating letters of 'lieuis' are 'lei'.
'lei'+'sure'='LEISURE'
Can you help me to learn more?
(Other definitions for leisure that I've seen before include "Spare time" , "R&R" , "Free time; relaxation" , "time-off" , "casual wear" .)