Ramble or return before midday (4)
I believe the answer is:
roam
'ramble' is the definition.
(I know that ramble can be written as roam)
'or return before midday' is the wordplay.
'return' says the letters should be written in reverse.
'before midday' becomes 'am'.
'or' back-to-front is 'ro'.
'ro'+'am'='ROAM'
(Other definitions for roam that I've seen before include "Move about aimlessly" , "Rove or ramble" , "Ramble without purpose" , "Peregrinate" , "range" .)