Opening time in a country bar came at last (8)
I believe the answer is:
aperture
'opening' is the definition.
(aperture is a kind of opening)
'time in a country bar came at last' is the wordplay.
'time' becomes 't'.
'in' is an insertion indicator.
'country' becomes 'peru' (Peru is an example**).
'at last' indicates one should take the final letters.
The last letters of 'bar came' are 're'.
'a'+'peru'='aperu'
't' inserted within 'aperu' is 'apertu'.
'apertu'+'re'='APERTURE'
(Other definitions for aperture that I've seen before include "Opening, mostly small" , "Eye" , "'Hole, opening (8)'" , "Opening (for a photographer?)" , "Opening (on camera, for example)" .)