Time to get uniform fever? (4)
I believe the answer is:
ague
'fever?' is the definition.
(illness causing fever)
'time to get uniform' is the wordplay.
'time' becomes 'age' (an age is a period of time).
'to get' is an insertion indicator.
'uniform' becomes 'U' (phonetic alphabet: alpha, bravo, charlie etc.).
'age' enclosing 'u' is 'AGUE'.
(Other definitions for ague that I've seen before include "Malarial fever; chill" , "Illness with fever and shivering, malaria say" , "Fit of the shakes" , "Burning fever" , "Feverish illness" .)