Stop in time to have a beer (4)
I believe the answer is:
pint
'a beer' is the definition.
(beer is typically served by the pint)
'stop in time to have' is the wordplay.
'to have' says the answer is hidden in the clue.
'PINT' can be found hidden inside 'stop in time'.
(Other definitions for pint that I've seen before include "Quantity" , "Glass of beer (colloq.)" , "Standard measure of beer or milk" , "small amount" , "Liquid meassure - four gills" .)