Used to make drink when working late each first Friday (3,4)
I believe the answer is:
tea leaf
'used to make drink' is the definition.
(tea leaves are used to make tea)
'working late each first friday' is the wordplay.
'working' indicates an anagram.
'each' becomes 'ea' (abbreviation).
'first friday' becomes 'f' (1st letter of 'friday').
'late' with letters rearranged gives 'teal'.
'teal'+'ea'+'f'='TEA-LEAF'
'when' is the link.
(Other definitions for tea leaf that I've seen before include "might be spotted in China" , "One taking" , "One from Assam perhaps" , "Beat; sell" , "Part of plant used to make drink" .)