Post Office over time provides instruction to readers (3)
I believe the answer is:
pto
'instruction to readers' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'post office over time' is the wordplay.
'post office' becomes 'po' (abbreviation).
'over' indicates putting letters inside.
'time' becomes 't' (abbreviation).
'po' enclosing 't' is 'PTO'.
'provides' is the link.
Can you help me to learn more?
(Other definitions for pto that I've seen before include "See overleaf" , "Please turn over (abbr.)" , "Turn the page" .)