As soon as the figure is divided by a hundred (4)
I believe the answer is:
once
'as soon as' is the definition.
(I've seen this before)
'the figure is divided by a hundred' is the wordplay.
'the figure' becomes 'one' (I've seen this before**).
'is divided by' is an insertion indicator.
'a hundred' becomes 'c' (roman numeral).
'one' placed around 'c' is 'ONCE'.
(Other definitions for once that I've seen before include "... upon a time for the storyteller" , "In days gone by" , "not repeatedly" , "A single time" , "Cone (anag.)" .)