When vampires sleep in Drogheda yard (3)
I believe the answer is:
day
'when vampires sleep' is the definition.
(I've seen this in another clue)
'in drogheda yard' is the wordplay.
'in' says the answer is hidden in the clue.
'DAY' is hidden in the letters of 'drogheda yard'.
(Other definitions for day that I've seen before include "Unit of time" , "Lewis as poet" , "24 hour period" , "THIRD PART OF 23" , "24 23 acrosses" .)