Long period in Spain, working (3)
I believe the answer is:
eon
'long period' is the definition.
(I've seen this before)
'spain working' is the wordplay.
'spain' becomes 'e' (abbreviation for Espana).
'working' becomes 'on'.
'e'+'on'='EON'
'in' acts as a link.
(Other definitions for eon that I've seen before include "Prolonged period" , "Very long age" , "Vast period" , "Geological period" , "Immense period" .)