Pal drops in at random after lunch (12)
I believe the answer is:
postprandial
'after lunch' is the definition.
(postprandial means after a meal)
'pal drops in at random' is the wordplay.
'random' indicates anagramming the letters.
'pal'+'drops'+'in'+'at'='paldropsinat'
'paldropsinat' anagrammed gives 'POSTPRANDIAL'.
(Other definitions for postprandial that I've seen before include "type of speech?" , "After dinner" , "Immediately after a meal" , "Wet blanket" , "after eating" .)