Cover for a spell (4)
I believe the answer is:
span
This clue is a double definition.
'cover' is the first definition.
(I know that span is a more specific form of the action cover)
'for a spell' is the second definition.
(span of time)
(Other definitions for span that I've seen before include "Distance between bridge abutments" , "Complete duration" , "period of time" , "Measurement taken from an extended hand" , "Section of bridge" .)