Period of time — something magic maybe (5)

I believe the answer is:

spell

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'period of time' is the definition.
(spell is a kind of period of time)

I can't explain the remainder of the clue.

(Other definitions for spell that I've seen before include "influence" , "Words with magical power, or a period of time" , "Short time, splinter" , "Incantation; write in letters" , "JP" .)

I've seen this clue in The Times.

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