Bats he let feast -- they normally come out at night (5,5)
I believe the answer is:
false teeth
'they normally come out at night' is the definition.
(false teeth are removed over night)
'bats he let feast' is the wordplay.
'bats' indicates anagramming the letters (I've seen this in other clues).
'he'+'let'+'feast'='heletfeast'
'heletfeast' anagrammed gives 'FALSE TEETH'.
(Other definitions for false teeth that I've seen before include "set out at night" , "New gnashers!" , "Choppers that may be taken out" , "Denture's components" , "Plates" .)