Opening in a schedule (4)
I believe the answer is:
slot
'opening in a schedule' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slot that I've seen before include "Hole for e.g. coin" , "Space for inserting coin" , "Space for coin or programme" , "Opening for coin or TV programme" , "Small opening, for a coin say" .)