Suppose visitors to be out of time (5)
I believe the answer is:
guess
'suppose' is the definition.
(synonyms)
'visitors to be out of time' is the wordplay.
'visitors' becomes 'guests' (guest is a kind of visitor).
'to be out of' indicates named letters should be taken away.
'time' becomes 't' (abbreviation).
'guests' with 't' removed is 'GUESS'.
(Other definitions for guess that I've seen before include "Imagine" , "Hypothesis" , "Reckon" , "Estimate; suppose" , "Make stab at" .)