Rubbish on a schedule (4)
I believe the answer is:
rota
'schedule' is the definition.
(I've seen this before)
'rubbish on a' is the wordplay.
'rubbish' becomes 'rot' (both can mean nonsense).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'rot'+'a'='ROTA'
(Other definitions for rota that I've seen before include "List of people taking turns" , "Repetitious canon" , "Working times list" , "List assigning turns of duty" , "Roll call or roster" .)