Reckon attendees will waste time (5)

I believe the answer is:

guess

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'reckon' is the definition.
(I know that reckon is a kind of guess)

I can't explain the remainder of the clue.

(Other definitions for guess that I've seen before include "Surmise" , "Speculate" , "shot?" , "Speculation" , "Take a stab at the answer" .)

I've seen this clue in The Times.

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