First of lunches consumed behind schedule (4)
I believe the answer is:
late
'behind schedule' is the definition.
(I've seen this before)
'first of lunches consumed' is the wordplay.
'first of' suggests taking the first letters.
'consumed' becomes 'ate' (eating is a kind of consuming).
The first letter of 'lunches' is 'l'.
'l'+'ate'='LATE'
(Other definitions for late that I've seen before include "Not yet arrived - departed" , "Previous" , "Behind schedule" , "In arrears" , "Former; behind time" .)